122 



The Journal of Heredity 



on to a normal endosperm, to bring 

 them to maturity. Such an experiment 

 would show whether the lethal action 

 of the defectives is merely one of an 

 insufficient food supply or whether 

 other factors are involved. 



For the second group, a defective 

 which also appeared in the variety 

 Century Dent, is typical. In this type 

 the development of the recessive seeds 

 is halted only after a considerable 

 proportion of the endosperm tissue has 

 been laid down. It is impossible to 

 determine whether a plant is segregat- 

 ing for this defective until the seeds 

 have reached the soft dough stage, 

 while in the case of the type described 

 above the aberrant seeds can usually 

 be identihed soon after pollination. The 

 seeds of the partial defective are al- 

 most normal in size but lack the lustre 

 of fully developed kernels. The peri- 

 carp attains almost complete develop- 

 ment and since the endosperm fills it 

 only partially, the defectives have a 

 shrivelled appearance. They are read- 

 ily distinguished from normal seeds on 

 the same ear and separation of the two 

 types can be very accurately made. 

 The development of the embryo in 

 these abortive seeds is apparently nor- 

 mal in every respect and they show 

 a germination of eighty to ninety per 

 cent under optimum conditions. The 

 seedlings, however, are very weak and 

 under field conditions seldom emerge. 

 Even in the greenhouse most of them 

 die in several weeks. When the most 

 vigorous seedlings are "nursed" along 

 in the greenhouse and later trans- 

 planted to the field, it is possil)le to 

 mature a few plants. An ear from 

 such a homozygous plant is shown in 

 the illustrations. Apparently the lethal 

 action of this defective is purely one 

 of an insufficient food supply. 



This partial defective has been 

 crossed with the complete defective 

 which appeared in the same variety 

 and which has already been described. 

 The first generation of such a cross 

 was normal. In the second genera- 

 tion several of the ears were .segre- 



GERMINATING SEEDS 



Figure 13. This ncwlj' discovered type of 

 defective kernels is characterized by the fail- 

 ure of the embryo to go into a resting 

 stage. The growing embryo stretches the 

 pericarp and in extreme cases ruptures it. 

 These grains have a characteristic swollen 

 appearance, and are lighter in color than the 

 other grains on the same ear. When the 

 :ar is harvested the embryo in these seeds 

 dies from lack of water. 



