364 



The Journal of Heredity 



On account of the phenomenon of 

 double fertilization in maize, the F:; 

 endosperm develops on an Fi ear/ 

 The Fi plants are, as a rule, extremely 

 vigorous and the mealy seeds when 

 borne on a hybrid plant are appre- 

 ciably altered in appearance. There 

 is a partial development of the cor- 

 neous endosperm and the seeds are 

 often almost normal in size. The 

 white portion of the endosperm show- 

 ing through the incomplete corneous 

 layer gives the seed a dull and mottled 

 appearance. Seeds of this description 

 are often found on ears not carrying 

 the factor for mealy, especially when 

 the ear has ripened prematurely. Sep- 

 aration of mealy seeds after crossing 

 is consequently more difficult and less 

 accurate. 



It appears that the genetic factor 

 for mealy does not specifically inhibit 

 the formation of corneous endosperm. 

 It simply arrests the development of 

 the growing seed at a certain stage. 

 The horny layer which is apparently 

 formed later in the process is thereby 

 ordinarily eliminated. On the hybrid 

 plant, however, where the various 

 stages follow each other in more rapid 

 succession, the corneous endosperm 

 has an opportunity to become partial- 

 ly developed before the factor for 

 mealy can operate. Just how this 

 character would manifest itself in 

 floury types of corn in which the hard 

 endosperm is completely lacking is 

 not known, but it would presumably 

 result merely in a loss of size. 



A Lethal Factor 



Practically speaking, mealy is a 

 lethal factor because under ordinary 

 field conditions the mealy seeds will 

 not grow. When planted in the 

 greenhouse under optimum conditions 

 of temperature and moisture the re- 

 cessive seeds show a germination of 

 twenty per cent. The seedlings are 

 verv small and weak, as shown in 



the illustration, and survive but a 

 short time. Seeds from Fi ears have 

 a higher germination and produce 

 more vigorous plants, but even these 

 ordinarily live only a few weeks. 



Linkage Relations 



The linkage relations of this char- 

 acter were discovered quite by acci- 

 dent. In one of the Fi ears the mealy 

 seeds were so well developed that it 

 seemed feasible to plant a row of 

 them in the field in order to get the 

 character in a homozygous condition. 

 A week later when the seedlings had 

 emerged this row was easily the most 

 conspicuous feature of the entire field. 

 All of the plants were albinoes except 

 one. This solid row of white seed- 

 lings in sharp contrast to the rows of 

 green ones on either side made a very 

 striking demonstration of linkage. 



The other ears of this cross were 

 later tested for linkage and the data 

 are given in Table III. Figures for 

 only those ears segregating both 

 mealy and white seedlings are given. 

 Since only part of the seeds were 

 planted and since the germination was 

 never perfect, no attempt has been 

 made to reduce the figures to actual 

 linkage values and only the percent- 

 age of each type are here given. This 

 provides but an indication of the link- 

 age values, but in cases where it is 

 impossible .to back-cross the hybrid 

 vv^ith the double recessive, one cannot 

 arrive at more than a rough approxi- 

 mation. 



Table III. 



■* Webkr, H. J . Xenia, or the immediate effect of Pollen in Maize. Bullcthi 22. Division 

 of Vegetable Physiology and Pathology, U. S. Department of Agriculture. 1900. 



