DOMESTICATED PLANTS — BLAYDES 327 



{Tripsacum) ^ and from the hybrid or its segregates teosinte [Euch- 

 laena) resulted. The crossing of these two genera is difficult, but it 

 has been accomplished in a few instances by Mangelsdorf and Reeves, 

 by means of a special technique. The chances for it to occur in nature 

 are remote. However, teosinte has a set of chromosomes which appear 

 like those of corn and a set similar to Tripsacum. Taxonomists have 

 given teosinte the rank of a new genus {Euchlaena) since it is so dif- 

 ferent from either Tripsacum or corn. If the above story is true, we 

 have the unusual case of hybridization between two genera resulting 

 in a third genus of grasses. The early Indians did not make much 

 use of teosinte as a domesticated plant, but it is used now to some 

 extent as a forage plant. 



A CAUSE OF STERILITY IN SOME HYBRIDS 



Hybridization between two rather distantly related individuals of- 

 ten results in the hybrid individual's being sterile. This sterility may 

 be due to differences in the chromosomes from the male parent and 

 the female. These differences may not prevent fertilization's taking 

 place when the male gamete comes in contact with the ^^<g cell. If this 

 occurred in the day lily {HemerocaUis julva) the sperm would have 

 11 chromosomes and the egg would have 11 chromosomes. The ferti- 

 lized tgg or zygote would have 22 chromosomes or the diploid number. 

 There is no orderly arrangement of the 22 chromosomes within the 

 zygote nucleus. The zygote divides mitotically, resulting in two new 

 cells which are identical as far as the chromosomes are concerned, and 

 each is identical to the zygote from which it came. In the same way, 

 since the leaves, stems, and roots originate from the embryo by the 

 same kind of cell divisions, it becomes evident that all cells of the vege- 

 tative plant are identical. This is also true for the flower parts up 

 to and including the so-called mother cells of the anthers and ovules. 

 The mother cells are the immediate forerunners of the gametes. How- 

 ever, it is common knowledge that gametes (sperms and eggs) have 

 the monoploid number of chromosomes, or half the number found in 

 any cell of a leaf stem, or root. The reduction from the diploid num- 

 ber to the monoploid occurs in the first two divisions of the mother 

 cells in the anthers and ovules. The sperm of a day lily, as stated 

 above, has 11 chromosomes which we might label a, 5, c, d^ e, /, </, A, ^, i, 

 and h. An egg cell of this same kind of plant has 11 chromosomes 

 which are similar and could legitimately be labeled from aioh when 

 the ^gg and sperm fused. There is a random assortment of these two 

 sets of chromosomes in the zygote, and this is continued throughout 

 all vegetative or somatic cells to and including the mother cells of the 

 anthers and ovules. However, at this point, the chromosomes become 

 assembled in pairs within the mother-cell nucleus, a pairing with a, h 



326511—55 23 



