Part VII Identity of System Controlling Expression of ae and aft During the summer of 1955 when tests of of the behavior of amt were resumed, evidence was obtained indicating that an Spm-type element 1 was responsible for control of gene action at ag. As pointed out Je yO in the last section, the expression of this Spm element was obscure A “a m1 and this contrasted with the clearity of this in the ay cultures. However, several test crosses were made during the summer of 1955 eugewt ed . m~l the result$ of which i that the Spm¢ element in the a, OL Yphtbh ES Ceo wy 0. Bole cultures weutd control gene action at a") in ae-sharphy expressed a he HAT Te manner as it was doing in the aa cultures. Tests were then “3 initiated to determine if this could -be demonstrated, mou ° Leen mar (eo fuel ue aba tourrd peel ys ae © lactone ts Some of these teats will be owtiined below. % oth tug We pristors Meter, Me Yuring the summer of 1949, a plant that was homozygous for a swt had been crossed to one homozygous for the standard recessive, Ane On the ear this cross produced, there weremany uniformly pale colored kernels and some variegated kernels showimg spots or specks of Ap ina A . . colorless background. In 1950, some of the kernels on this ear were sown under culture number 9303, and those in 53030 were derived from pale colored kernels in which there were one or several colorless the areas within which specks of,Ao phenot,pe were present. One plant An, ples 7) ‘ in culture 5303C, plant number @, was variegated in that small streaks of the Ay phenot,pe appeared in a non-pigmented background. This plant was a" fa, in constitution. The first ear on the main stalk was self-pollinated. Among a total of 455 kernels this ear produced, “ ruth OER 150 were uniformly aale colored, 195 were variegated the pattern of tris oy a we my OB = 0: cul uw aon? Roay an le from one-that had spots of ie in a colorless background to Wood . ; wit 4 Mel ee am ges awl 1, caleyp VA i stir pele < ao tiny specks of ho» either throughout the kernel or #% restricted + A A 4 i colorless areas in an otherwise pale-colored kernel. In addition, there were 110 colorless kernels. An ear of a tiller of this plant was used in a cross with a plant homozygous for Bos This ear was sectorial with regard to the expression ofa," Nearly all the Mis, S aut kernels within a well defined sector, extending a distance of S . < about 2/3rs of the ear and covering several rows were uniformly pale on A % colored. Only 3 kernels within this sector were variegated. “hey had. i tiny specks of the Ay phenotype in a colorless background. On the wae lp ae Kote A foe s Ma rest of this ear, the ag -1 . Kernels segregated inal: 1 ratio e#-- Jj ok 4b, ‘io yd he are te uniformly pale colored tp’ variegated. Among the veriegted kernels, 4 a CFL ey the pattern of Ap mutant areas ranged from spots | of ne in a colorless SS Ved epeebeid Lay Hing av habe LIC ile ie ap bins eee nee in some kernels to specks of this in other kernels. ' Poblen A of plant 5303C-2 was placed on the silks of a 4. pian gf Romozygous for ao, ’ f fh oR i mune Among the ast carrying kernels on the resulting ear, a ratio of A 1 uniformly pale colored kernel to 1 variegated kernels appeared and among the kernels in the Aayriegated class the patterns of variegation,were similar to those of the reciprocal cross, just described. Kernels from this ear were sown in the summer of 1955 under culture number 6908. Tests conducted with one plant in this culture will be described. Plant 6903A-3 was derived from a pale colored kernelg on the ear mentioned above.. The-piant-proved-te—be-varicgated in thet+—very—small streaks of—A5--appesred-in a non-pigmented background. Pollen of this plant was placed on the silks of ears of three different plants each homozygous for Boe Iwo of these three plants were belonged to the regular Ao tester stock. The third had quite a different history. It was derived from a colorless kernel on an eur produced by the m-1 cross of the the original plant carrying ay to a plant that had a 2 but was homozygous for Al: The original a7 carrying plant was Ey ate arkue 7 ~ a," ‘ay: Ay/25 in constitution and it carried a number of Spm elements. ae Men Lusk of ab The colorless kernels on thé ear, should | be a/ay and either A /a, 1 Wy WO.C WA ew oe C1 muse swe or A, /a, in constitution, and ++. should heve sevepeai Spm elements, in=it. Alay The plant tovwkich the cross with plant 6903A-3 was made—preved -+to—be a . A,/ &) » as later tests showed, The types of kernels on the ears Ww with produced by crosses with the Bo tester plants and,this a, plant were aA strikingly different. Among the 482 kernels on the ears produced by va! e m—1 kernels were uniformly pale the fopmer cross, all but 23 of the a5" A colored. Uf the 23 odd kernelgs, 11 were variegated for small specks of the Ay phenot. pe in a colorless background and 12 were sectorial for such areas in an otherwise pale colored kernel. Among the 383 kernels ( teas‘lay doen) produced by the latter cross, 183 wére totally colorless and 200 were A ay.) rl 1 See er. Wr; MA as AS cme’ Cf. t ya ae variegated , and the pyptern of variegation’ was similar, among-ati 2 ako: iS kernels, expressing—it. Spots of the A, phenotype abbearéd in a colorless background (Photo. ). It was suspected that the Spm olin Yr “bs Tages Aw Wee. je elements in the an/ay parent of this cross was responsible for the Jt uniformly expressed variegated EBxpxXEEsxuuxefxax pattern in these kernels and that the” Spm elements im—tt were the same as those that control gene action at amt. Therefore, both x= variegated kernels and colorless kernels on this ear were sown in the summer of 1956 under culture number 7113 and tests 4 of the plants derived from thea were commencedygin order to obtain evidence for the Supposed identity of the system responsible for control Bia im Aen pay! yi m~1 m-1 of ay and a, * A Plants derived from variegated kernels on the ear just described were sown under culture numbers 7113A and 7113 B. Those derived from the colorless kernels were sown under 7113C and 7113D. A number of different types of test were conducted with the plants of culture 7113 on ett} Included among them were crosses of the a,7- ‘Jay plants in A and B of 2 wad \ ‘ stoudord culture 7113 to plants homozygous for a, derived from the tester stocks. “A Kh These—tester plants were A)7A, in censtitution. The types of kernels appearing on the ears produced by these test crosses are entered in table l. Some of the plants in culture 71137 were also crossed by plants homozygous for a7 (state 5718) and for A, in which no Spm was present. This was done in order to determine the constitution f uy a of the plants in culture 7113 with respect to AL and also the presence Conk ufibas, heluauren sue in them of Spm elements capable of abtering ay in the manner. in cbalture 7113 Some plants, proved to be Af /Ay and others proved to be Aj /ay. In all ““ plants of the latter phenotype, one or more active 5pm elements were olin a, hire Ape are present as shown by the kernelg on tars so produced, entered in table 2, A A : wht Comparison of ratios of uniformly pale kernels (no “pm present) to we , Ale ° ALL oe jean! x ov - - variegated kernels ( Spm present) for a5" 1 and a,” 1 wnere-thie-eo=td A p A A we ay rh dy © SYM be-made is summarized in table 3. Confermity ef ratio: ef types-is WA, ‘yan teh . evident. ply wy . m-1 m-1 In order to Woneda evidence ef Spm control of both an and a, e a kernels were selected from ears of some of the crosses entered in table 2 and plants grown from them in the summer of 1957. These plants were tested in various ways, new—te—be-deseribed. The phenotypes of thoe kernels that gave rise to the plants that were tested, as well as the number derived from each type, are shown in table 2 along with the 1957 culture number given to them. A description of these tests will commence with the plants in culture 7299 derived from the kernels on the ear produce by plant 7113C0-5, table 2. From the ratio of pale colored to variegated kernels on this ear, it could be concluded that 7113C-5 carried one active h) ae pea} Spm element. All plants derived from kernels on this ear should be pp NP “ an /a,» A/ay- Those derived from the uniformly pale colored kernels h should have no active Spm element in them whereas those derived from the variegated class of kernels should contain an active Spm element. All plants derived from the pale class of kernels were themselves uniformly pigmented, indicating the absence of an &ctive Spm element in them. All plants derived from the variegated kernels were variegated for small streaks of she A, phenotype in a non-pigmented background, indicating the presence in them of an active Spm element. To test for the response ofa”) to-sither the presence or the absence of the Spm element that . n= . controls gene action at A 1. one or more ears of each plant were used in a cross with A, /Ay plants that were either a m1 ay or aml /_ ml Qh in which no evidence of the presence of an Spm element was given either Spouoleg by the appezrance of the plant: or by the of kernels on ahetnto, S Yoo ears produced by crosses of one would respond. no variegated kernels appeared. A1l1,26 plants derived from variegated kernels were themselves variegated for streaks of the A, phenot’pe ina non=-pigmented background. The ears produced by 25 of these plants in erosses with the ast tester plants indicated the presence in each of ~~ a NS one or more active Spm elements capable of controlling gene expression at ayn One fully active Spm element was present in 11 plants, two such elements were present in 8 plants and three or more were present in ON wa Mel j JTW 6 plants, the number of Spm elements being given by the ratio of 4 uniformly pale colored kernels to variegated kernels among these that Bs, were ayn /ay/ay in constitution. A The two exceptional plants, mentioned above, are important for this GL study for tkeyx the tests conducted with them and with their progeny serve to confirm the precise control of a," and at behavioy ky and in° o Wank ‘a Whe G hae yo \yoh © the same manner foreach by qne- particular “pm element. One of the 3 ~ plants, 7470A, derived from a uniformly pigmented kernel on the SS ®, ear of plant 7113D-5 (table 2) had an Spm with altered action. It ~~ . ke proved to be Spm-w that undergoes frequent but late occuring changes to x y s Spm-s. The second exce*tional plant, 7467-1, derived from a variegated ~ kernel on the ear produced by plant 7113C-8 (table 2), carried an Spm fe oy SS . oO a way AM The element that was undergoing cyclical change to—the—inaetinve. phase. A types of test conducted with these two plants and with their progeny 10 will be considered at the end of this section. Slants 7113B-1 and B~$, table 2, were A/a,» as” /a, in constitution. From the ratio of yarkeguked pale to variegated kernels on the ears produced by the cross entered in this table, two or more active ‘Spm elements were present in each. Tests conducted with the plants derived from the uniformly pale colored kernels and from the variegated kernels on these ears will now be considered. The 11 plants derived from the uniformly pale colored kernels were themselves uniformly pigmented. \\ fifteen test cross ears were obtained from these g plants, the type: of cross being the same as that outlined above. On each of these ears, all ayn ty ay /ays ag /asn Jay, or ast fase t/a ge kernels were uniformly pigmented. None were variegated. Of the 8 plants derived from the variegated kernels (culture 7298, table 2) all were vuriegated. On the 10 testcross ears obtained from them, both uniformly pale colored among those that were either homozygous for ayn or heterogyggus for it kernels and variegated kernels appeared, ' the-ratie of these two—types From the ratio of these two phenotypes on the di ferent ears, it was } concluded that t active Spm element was present in 5 plants, two active ox Spm elements were present in 3 plants, and Hor more active Spm elements were present in umgz l plant. Again, these tests showed that plants having -1 no Spm as judged by a,” behavior had no “pm as judged by all behaviorg 1l m—1 and those having Spm as judged by a) behavior likewise had Spm as m-1 judged by a5 behavior. Extensive tests were made with plants derived from the Ay» Ay kernels entered in table 2. these kernels were selected from ears of m—1 3 in then. Each selectdd kernel plants in culture 7113 that had a had an area in it in which Any delivered by the male parent , had been Me Open as WU pas Anchen. Eee. AES ite v ¢ \ m=1 2 Lost, this allowed the presence of a ate Qe ergot wt ‘ parent, to be revealed. In 17 of these kernels, this area had spots of » delivered by the female Ay in a colorless background, indicating the presence in the kernel of both aut and of Spm. In one kernel, the a jut area was uniformly pale colored, suggesting that this kernel had received ast from the female parent but no “pm element. “hus, all 18 plants derived from m-1L 1 these selected kernels should be A/a, in constitution and ? Ap / a5 in 17 of them, Spm also should be present. Each of the 17 plants He ca anee! NM Ut in which Spm was present were used in making crosses with plants n~ homozygous for A, and for a 1 9 in which no Spm was present and also with plants that were Agmozygous for ay and As and/or homozygous for a," and Ay in which no °pm was present. The phenotypes of kernels on the ears produced by test crosses of each of the 17 plants are entered in i iP . table 4,” The Spm constitution of each is summarized in table 5. 12 Only two of the 17 plants had t Spm element in them. All other ape plants had more than DPD Upm-slemens. In one of the two plants having om : m-1 ay idta Ht close to ay Spm element, plant 7296A-2, this Spm element was located,in chromosome 5. It will be noted that the-disecrepgncy in ratio of uniformly pigmented difhe caf kernels (no °pm) and variegated kernels (Spm present) is very mete in werk m-1 Ww -1 | m1 the tests of a, and a5" , behavier. Plant 7296A-2 was a, Pr/ 4 A rLous Ye ee Dg a5 pr in constitution. The a7 tester plants used in making crosses _ (’ adres s AKL a): cy we Unt tunis Ww ah with this plant was homozygous for pr. On these ears, the distribution pale % of Pr and pr to the uniformly,pigmented kernels and the variegated kernels ~ A indicated that the single “pm in plant 7296A~2 was located in the chromosome 5 carrying Pr and at a distance that was approximately 30 a4 ayaXs nh ~ crossover units from Pr. The percent crossing over between Pr and Ay “A is approximately 28 percent. Thus, the evidence from the two sets of "Mal be F| test crosses placeq Spm very close to aj in plant 7296A-2,. Flant 7297A-2 had 2pm elements in it. It was Wx/wx and in the cross with the ayn yam, no Spm tester plant that also was wx/wx, linkage of one of the two Spm elements with Wx was made evident. Among m-1 the kernels on—the-kerriets on the ear that were homozygous for ay there were 111 pale colored kernels (no Spm) of which 27 were Wx and 84 were wx. Among the 288 variegated kernels, 167 were Wx and 121 were wx. 13 was given . In tests of plant @468A-2, evidence,of the presence of 3 Ypm elements tested in the cells that gave rise to ear of the two,ears, this plant. Pollen collected from a tassel of this plant was used on silks of ears of plants that were Al/A,, a,/a, no Spm and also on ears of plants that were a m-1 / 1 2 2 1 m=1 ay ’ An/Ay in which no Spm was present. The ratio of variegated to pale kernels on the ears these plants produced indicated that in the part of the plant that produced the tassel from which pollen was collected, only 2 Spm elements were present. Plant 7298A, derived from an Ay» A, kernel in which an area was 2 present that exhibited a pale phenotype was suspected to be A/a™, m-1 at active A,/ ao in constitution in which no,Spm element was present. It was “A used in crosses with plants that were AVAL» an/ay in which no Spm was present and with plants that were at /a,™", A,/A, in which no Spm was present. On the ears produced by these crosses, no variegated kernels appe:red, A and C, table 6. In order to show that the ayn in this plant would respond to an active Spm element, the ear produced by the main stalk and an ear of a tiller were used in crosses with plants homozygous for AL and ay in which 1 Spm was present. (For tests of the preseyce of one Spm in each of these plants, 7308D-1 and 7308D-2, see page -) The types of kernels appearing on each of these ears is 14 given in B of table 6. It was clear from-these tests that plant 7298A haa no active Spm element in it to which either amt or ast could respond. i ap umpe A Itwas-also evident that the ast in this plant would have respnnded to Spm had it been present. It was also known that the amt delivered by the amt no Spm tester stock would have responded to Spm had it been 3 present as these same tester plants had been unsed in many other crosses an these had clearly demonstrated its capacity to respond to Spm ~- Hdl ur Altogether, 121 plants were tested in the summer of 1957 fer the Vrcl tb the “I AY Sy Y Wh > ule wAWH, sono * PesPonse of ant and Ay 1 to the presence—-or-absence. of-Spm wren N ‘the selection of plants to be tested for its presence or absence was based on the known response of only one of ca gt either a7? or ast, Te ck ne rene (WWM it oot were quite ne tothe yr In all tre0:0h the-response of m=) - ricouk 'o Ney utd oar om bo DAM oN we dak, A“ presence or absence of Spm, and to the number of them,-if present. There were no exceptions to this. The two plants among the 121, plant 6467-1 and ee which a single Spm with modified action was present only m—-1 served to strengthen the evidence of the common type of response of ay . ong i Co femede Gut Wha and a5" 1 to the same Spm element. Vou'n 7 (°# Vincany Wee ye Uap aaa Plant 7467-1 was derived from a variegated kernel on the ear produced by plant 7113C0-8, table 2. Its constitution was an /a,, A,/a jo (spotted). The plant derived from it was expected to be variegated for 15 Ay streaks in a non“=pigmented background. The main stalk of the plant, however, was uniformly pigmented aw if no Spm were present in ‘dab the hoa plan wan of uml tiller ,—howexer, was-—seetorial--fer areas in which small streaks ce A appeared in a non~pigmented background. eat ih median aainelil \ “kui . ay Tb? | We Pic Case} WwW deel suggested that Le hed an inactive Spm element im—t that ‘was undergoing A change to the active phase in some cells of the tiller. The silks of the first ear on the main stalk received pollen from a tester plant that was Ay/Ay» a,wt (early) Bt/a,™ (1ate) bt in which no Spm was present. Among the 393 kernels on this ear, 193 were fully pigmented, that is, Ans and 200 were ann /ay/ay Among the latter, 133 were uniformly pale pigmented, as if no Spm were present in them, and 67 were variegated. However, in only 4 of these 67 variegated kernels was the type of variegati that expected t§ appear in the presence of a fully active Spm element. In the remaining 63 kernels, Spm was active only in a sector in the kernel (small specks of Ay in a colorless area of an otherwise pale pigmented kernel) or was weakly active throughout the kernel ( small specks of Ay in a colorless background throughout the kernel). The silks of the ear produced by the tiller received pollen from a plant that was A,/as ay” (spotted) Bt/a, bt in which no Spm was present. .~ There were 156 kernels on this ear and 49 of them were fully pigmented 16 (Ay > Ay}. In addition, there weve 83 kernels that were either colorless or pale pigmented and 24 that were variegated. Among the latter, 7 Va, Qoen were variegated for spots of AL in a colorless background, 11 had spots t a ad of Ay in a colorless background, and 7 had a type of variegation that could be expected if the kernels excecepichtepBthbenpcecesbch hag nettior fh _ ee AB aay: fn Linke" Reh 7. uae wD, as m1 tHe anthem but-omey a, and a5 4 Sth undergoing mutation to ats \ luc { Ay and Age The cross was made to obtain just these kernels in order a to test the kehuxiarxsf? type of response of at and a? to the some Spm element in the plants derived from el From the ear of the main stalk, seven plants were grown from ke nels that had small Ay specks in a colorless background under culture number T5774 and 3 plants were grown from the 4 variegated kernels in which a fully active Spm element appe»red to be present under culture number 757785. All 7 plants in culture 7577_A were darkly pigmented except for a few areas in which pigment was absent, and in some of these areas, small streaks of the A, phenotype appeared. Obviously, these plants had an Spm element in them that was undergoing change in phase of activity, from in-active to active in some cells during the development of the plant. XEXEBNLYARLFXMBAEXGLXLMEXKXARLSXINXERETEXWEKe The appearance of the 3 plants in B of culture 7577 were similar. Thexz plants in both A and B 17 Pura’ Vs) el of this culture were tested by cresSes with plants homozygous for a m-1 1 4h nN in which no Spm was present and with plants (state 5719A-1) and Ay homozygous for AL and a5 in which no Spm was present. The appearance of the kernels on the ears these crosses produced argz is shown in table 7. It was obvious that the Spm element in each of these plants was behaving as it had done in the parent plant, 7467-1. It was in its inactive a yp phase during much of the early development of the lant, turniag< to the 4 mw per. active phase in some cells only late in development. The response of both amt and ast to the activity phases of Spm was exactly alike. four plants were grown under culture number 7578A from kernels on the ear of the tiller of plant 8467-1 that appesred to nave Spm and - -1 -1, m- -1 - -1 and both a," 1 ane a5" ( ay” Ja,” */a," or a,” ‘/a,/a and a5 /ao/ a ay). In addition, six plants were grown under culture number 7578B from kernels that were uniformly pale pigmented, the type of pigment indicating that they were A,, an” /a,/ay in constitution. The six plants in culture 7578B will be considered first. Five of them gave no evidence of the presence of Spm in them either from the appea:ance of the plant or from tests that were conducted with each. One plant, 7578B=4, however, had a few sectors in which small Ay streaks appeared in a non-pigmented background. The remainder of this plant was uniformly pigmented, 18 It was obvious that this plant had an Spm element in it that was in its inactive phase in most parts of the plant, turning to the active phase in « few cells rather late in development. Thus, the pattern of %pm activity resembled that in the parent plant, 7467-1. The first ear of plant 7578B-4 which was A/a™", as t/a, in constitution, was used in a cross with a plant that was homozygous for Ay and ay in which no Spm was pre-ent. On the resulting ear, there were 210 uniformly pale pigmented kernels, 215 totally coloriess kernels, and one kernel that was variegated in part.- three-quarters of the aleurone layer of this kernel had spots of Ay pale in a colorless background and one-quarter was uniformly, pigmented. this was the only kernel on the ear that gave evidence of the presence of k Spm in the—femate-parent. The Spm in this kernel had changed from the inactive to the active phase early in development of the endosperm. The second ear of the main stalk of plant 7578B-4 was used in a cross with a plant homozygous for a," (state 5719A-1) and for Ay in which no Spm was present. This ear produced 460 kernels, half of which were homozygous for a7. In 79 of these latter kernels, evidence was given of the presence of Spm in them but in none of these kernels was Spm fully active. . In most of them, Spm had changed from the inactive to the active phase rather late in development of the kernel. 19 Two mther plants in culture 7578B were tested for the presence in them of an inactive Spm element by crosses of each with plants thit were homozygous for Ay and ao in which one or more active Spm elements were present. The usefulness of this test for revealing an inactive Spm element has been descrbved elsewhere. An ear of plant 7578B-2 was used in a cross with a plant of the constitution given above in which one active Spm element was present (plant 7538-4, see page ). On the resulting ear, there were 212 totally colorless kernels and 226 kernels carrying ayn. Among the latter, 152 were uniformly pale pigmented and the 74 were colorless with spots of A, phenot:;pe and in nearly all of them large areas exhibiting the pale phenotype also were present. Had plant 7578B-2 carried an inactive Spm , half of the variegated kernels would have had no pale areas or oniy a few small pale areas. It could be concluded, then, that plant 7578B-2 had no Spm element in it. This same conclusion was drawn from a similar type of test of plant 7578B-—3. An ear of this plant was used in a cross with plant 7538-6 which was homozygou for AL and a» and also for Spm ( see page for discussion of the constitution of this pl:int). On the ear produced by this cross, 196 kernels were totally colorless and 186 carried asm, Among the latter, 22 were uniformly pale pigmented and 164 had spots of Ay in a colorless background. In the majority of the variegated kernels, large pale areas 20 Obviously, plant 7578B-3 had no Spm element in it. also were present. / Thus, of the six tested plants in culture 7578B, oniy plant number 4 gave evidence of the presence of Spm in test crosses with either or both m=-1 m-1 ay and ay . Hach of the four plants in culture 7578A had an Spm element in it. The kernels that gave rise to these plants were selected from the tiller ear of plant 7467-1 because the “pm element in each appeared to have undergone change in phase of activity considerably earlier than in the other “pm carrying kernels on this ear. If this change from inactive > to active phase had occurred before gamete formation, an Spm with a new > Mm pattern of cyclical changes in phase of activity could be expected to } a xs a ? appe:r in the plant derived from a kernel in which this had occurred. XS This proved to be the-ease for two of the four plants in culture 75 78A The tests conducted with each of these four plants is shown in table 8. In plants number 1 and 2, the Spm element in e-ch underwent change in phase from inactive to active in a manner that resembled the pattern of In plant number 3, Spm Ve this givenby-i+ in the parent plant, 7667-1. ahd A was active in most parts of the plant, undergoing change to inactive in nN In plant number 4, Spm was ge - pint wih a ay: aur a few cells, early in plant development. years , active in all parts of the plant, undergohng change to inactive quite A A A late in development, and—eniy—in-some—celis . 21 The described tests of the progeny of plant 7467-1 clearly indicated 1 m= m-1 1 and a5 that both a would respond #kxke in like manner to the cir lane a wah, ol cpoe activity phase .of-Spmand tke change¢ in thie that occurs in a plant or, “a kernel. Thus, these tests serve as an additional proof of the identity of the system controlling gene action at a7 and aywt, Similar evidence was obtained from tests of the progeny of plant 7470A-5, to be described below. Plant 7470A-5 was derived from a uniformly pale pigmented kernel on the ear produced by the cross of plant 7113¥-5 (table 2). *t carried an Spm element but the action of this elementswas weak (3 pm-w) in most parts of the plant. Vhange from Spm-w to Spm-s occurred in some cells but only late in development. of the plant and of the endosperm tissue. this plant was aa (state 5718)/ a,» A,/a, in constitution. The first ear of the main stalk was used in @ cross with a plant that was ALA}: ay” /a, and in which no “pm was present. The state of aut was one that gives early occurring mutations to A, and to colorless in the presence of a fully active Spm element. On the ear this cross produced, there were 127 kernels that were uniformly deeply pigmented (A,) and 69 that were totally colorless (a,/a,/a,). There were 64 kernels that were apn t/a,/2, in constitution. “hirty-three of them were uniformly pale pigmented and 31 were variegated. kexrtyxerxthe In only one of the latter kernels was the pattern of variegation that which appears when a fully active Spm is present (see photo. )f In all other kernels, only small siots of the Ay phenotype appeared in a colorless background (photo. ). Nine plants were grown from these kernels under culture number 7580A. The single kernel that had large A, and colorless areas (RpmxExtyxE variegation pattern with Spm-s) was sown under culture number 7580B. This plant, however, died during the very unfavorable growing condutions of the spring of 1958. “he types of test cross conducted with theplants in culture 7580A are 1 shown in table 9. Each had an Spm-w element in it. Both a7 and a5. responded ah like manner to this %pm-w element. The state of ant used in the test cross gives only one or a few spots or specks of Ay or none at all in the presence of Spm-w. In the presence of Spm-s, it gives many small spots of Ay (compare photo. with photo. )o The state of asm? responds to Spm-w by producing a number of small spots of Ay in a colorless background. With Spm-s, it gives many large areas of A, as well as a 2 number of smaller areas (compare photo. with photo. ). On all testcros with ears, some kernels were present iM*WHZSGK sectora &88SSRHS¥d within wnich a pattern of variegation appeared resembling that produced by Spm-s 23 (photos )e The time during development of change of “pm-w to °pm-s was so late that very few kernels were produced that exhibited an opm-s type of response of a," or ast througuvcuy the kernel. Nearly all such changes occurred during endosperm development, and the majority of these took place rather late in its development. Evidence of this was m~1 m~1 given by the response of both ay and oo) to these changes in degree of activity of Spm. The ear of the tiller of plant 7470A-5 was used in a cross with a plant that was A,/ayzs ay” | (spotted)/a, in which no Spm was present. On fhe ear this cross produced, there were 58 fully pigmented kernels (A and 1 Ay), 133 colorless kernels, 32 lightly pigmented kernels and 62 kernels tha had spots of deep pigmentation in a colorless background. Among the m-l A variegated kernels, 10 appe:red to be ay ’ 2 in phenotype, 11 appesred to be Als ayn in phenotype and 41 were nearly totally colorless, only a deep pigment being small spot or speck of memxmr being seen in these kernels. Six plants were grown from the variegated kernels that appeared to be a,™, Ay under culture number 75814 and five plants were grown from the kernels that were nearly colorless, under culture number 75818. All plants in A of this culture were variegated in that some small streaks of deep anthocyanin pigment appears in a non=pigmented background. “he phants in 24 B of this culture were nearly completely non-pigmented. Only an occasiona very small streak of anthocyanin pigment appeared in them. The test crosses conducted with the plants in culture 7581 and the results obtained © from them are entered in table 10. In three of the five tested plants in A of this culture, one Spm-w element was present. It was behaving much as it had done in the Spm carrying parent plant. Vhanges from Spm-w to Spm-s -1 were occurring but only late in development. Plants 758lA,and A-4 had 2 Spm elements in then. One of these wad the Spm-w state and the other was Spmes. this latter appeared to be undergoing change in phase of activity from xmactive to inactive in some ce ls, late in development. Lhe four tested plants in B of culture 5781 all had an “pm-w element i: them and it was behaving much as it had dome in the paient plant. These plants probably were amt, amt although tests for this were conducted only with plant B-4, The Spm-w in these plants was changing to Spm-s in some cells of the kernels having it but usually, only la e in developmen of the kernel. In temtsuxef plant 57B1B-4, tests were conducted of the m-1 m=-1 response of ay to the Spm in it. The states of each were A and Bo much alike and the pattern of spots each produced in the kernél in the presence of the “pm in this plant was much alike. Each produced oniy a few deeply pigmented spots in the presence of the Spm-w element in this plant. Also, each responded in like manner to change of “pm-w to Spm-s. 25 1 m-1 With both a,™ 1 » Spm-w reduces the frequency of occurrence of and a5 mutation in comparison to Spm-s and also retards the time of their ‘ occurrence. With the two ant states examined ( eurly and spotted) the effect produced by Spm-w was the same as that which given by similar states of a,™?, reviewed in section IV. m-1 1 The common response of ay and a5 to the same Spm elements was reve:led by other tests conducted during the summer of 1958. In all 1 cases, both ay and ant responded in like manner to the Spm element or elements in a tested plant. Since the tests reported in this section - need reveil this common respo::se, the additional tests wxxl not be reviewed here