Haploids 437 



by their size, flowers, or leaves. The haploid, though, had smaller 

 stomata, very poor pollen, and smaller fruits, and rarely pro- 

 duced seeds. Haploid sporophytes have been found in tobacco, 

 tomatoes, maize, rye, Datura, wheat, sorghum, and other plants. 

 Haploid animals that are normally diploid have occasionally 

 been produced by drastic changes in their environment. 



Although haploids are highly sterile, they are theoretically 

 not completely so, for no matter how many chromosomes they 

 have, a certain percentage of their eggs and sperm should con- 

 tain a haploid set of chromosomes. In a plant that is normally 

 a true diploid, no gametophyte with less than a haploid set of 

 chromosomes will survive. If an egg with one complete haploid 

 set should be fertilized by a sperm which also has n chromo- 

 somes, a normal diploid organism would be produced, just as it 

 would if two normal, haploid gametes from a diploid organism 

 should unite. However, this diploid organism that comes .from 

 a haploid, except for possible gene mutations, will be homozy- 

 gous for all its genes. Thus, if haploids could be produced at 

 will, homozygous diploid organisms could be produced with rela- 

 tive ease and much more readily than by a program of in- 

 breeding. 



If the "diploid" that gave rise to the haploid was not a true 

 diploid, but an amphidiploid such as we describe in the next 

 chapter, the offspring would be different. From a haploid of 

 Triticum vulgare pollinated by a diploid wheat. Sears obtained 

 thirteen plants which had 40 to 42 chromosomes. Only two of 

 the 42-chromosome plants had all bivalents; the other eleven 

 had one or two univalents. Four of the eleven plants had one or 

 two trivalents, and one of the plants with a trivalent and one 

 other had a ring of four chromosomes. One of the 41- and one 

 of the 42-chromosome plants, when selfed, produced nullosomics 

 among the offspring. Such 2/1 — 2 plants could not be found in 

 a normal diploid. 



Numerous attempts have been made to produce haploid ani- 

 mals, and various methods to induce an egg to begin develop- 

 ment when it has only one nucleus have been successful. Usually, 

 however, the haploid individuals which resulted are abnormal and 

 survive only a few weeks. One individual of the European 

 newt, Triton taeniatus, survived to the one hundredth day of its 



