POLYPLOIDY 227 



physiological response. When diploid varieties were pollinated 

 witli such grains, a few triploid plants were obtained among a good 

 many diploid ones. According to de Mol, abnormal physiological 

 states possibly play a larger role than has generally been allowed 

 in causing chromosome doubling in other genera. The actual 

 mechanism at work in Hyacinthus still awaits discovery. 



Haploids. It will be convenient here to consider the question 

 of haploids, although strictly speaking such plants do not belong- 

 to such a discussion as this. The appearance of haploid individuals 

 among diploid forms is very rare. The first known case of such a 

 phenomenon in Angiosperms was found by Blakeslee and his 

 co-workers in 1922 for Datura stramonium. They have since 

 obtained several such plants. They were of very much weaker 

 growth than the diploid forms, but these workers succeeded in 

 growing them to sexual maturity. Later, Clausen and Mann 

 reported the presence of two haploid plants in their Nicotiana 

 tabacum hybrids. Gates has also recorded a single haploid 

 Oenothera among his cultures. This plant occurred among the F^ 

 hybrids. Reciprocal crosses were made between (E. rubricalyx, 

 and CE. eriensis, both of which have 14 chromosomes. (E. ereinsis X 

 Q^. ruhricalyx gave a uniform F^ generation, wdth the red pigmen- 

 tation of ruhricalyx and the flowers of eriensis. These bred true 

 in F2. The reciprocal cross, (E. ruhricalyx X CE. eriensis, made at 

 the same time, produced seedlings yellowish in colour and which 

 developed little chlorophyll and then promptly died when their 

 stored food was used up. The striking non-viability of this cross 

 led to its repetition, with the same result. From another capsule, 

 obtained by crossing different individuals of the same two species, 

 85 seedlings were obtained, which also behaved in the same 

 way, with the exception that two of the seedlings survived for a 

 time and one was planted out. The latter reached maturity and 

 belonged to a new type. It was very much dwarfed and com- 

 pletely sterile as regards pollen and seed production. This plant 

 proved to be a haploid and possessed seven chromosomes in its 

 somatic cells. It showed the red pigmentation of ruhricalyx. Its 

 leaves were narrow and rather pointed, and these were at first 

 thought to be characters belonging to eriensis, but they are more 



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