Haploids 435 



so. Sorghum plants have been found with only ten chromo- 

 somes instead of the usual number, twenty, and with ten uni- 

 valents in most cells. At anaphase all possible types of separa- 

 tion were found from five to each pole to ten to one and none 

 to the other, with the four to six and three to seven distributions 

 very common. In these plants, however, occasionally one, two, or 

 three bivalents were observed in a nucleus, and about 10 per 

 cent of the nuclei had bivalents. In pepper haploids twelve uni- 

 valents were often observed (Fig. 121), but in other nuclei there 

 were one to six bivalent associations. It has even been reported 

 that in three plants of Triticum monococcum there is no chro- 

 mosome pairing in prophase but that at diakinesis, the chromo- 

 somes may be in chains of varying lengths up to the whole seven 

 chromosomes. These configurations are lost by metaphase and 

 in only about 2 per cent of the microsporocytes are there any 

 bivalents. 



Where the haploid condition has become established as a regu- 

 lar feature of one phase of the life cycle there is not necessarily 

 any advantage or disadvantage in the haploid condition. In 

 fact, in such organisms there may be no resemblance in any 

 way between the haploid and diploid generations, that is, one is 

 not merely a small or a large version of the other. In some of 

 the lower plants the haploid and diploid generations are iden- 

 tical; in others they are very different. In some lines of evolu- 

 tion the haploid generation developed more prominently than 

 the diploid, but in other lines the diploid stage became more 

 prominent and the haploid generation became extremely small 

 and inconspicuous. Here, however, the haploid is not merely a 

 feeble version of the diploid, but it has become established as 

 something that is different in kind from the diploid generation. 

 However, when a haploid develops as an aberrant form of a 

 stage that, is normally diploid it is usually somewhat less robust, 

 less vigorous, and smaller than the corresponding diploid, and 

 frequently very much inferior. Miintzing, for example, has found 

 haploids of Triticum vulgare, Hordeum vulgare, Phleum pra- 

 tense, Dactylis glomerata, and Poa pratensis, and he says that 

 they are all "rather conspicuous by their small dimensions." In 

 pepper hybrids, on the other hand, Christensen and Bamford 

 report that it was very difficult to distinguish the haploid plants 



