1929] Navashin: Triploidy in Crepis 389 



process discussed above. This suggestion becomes still more probable 

 if one recalls the occurrence of haploidy in Crepis recently discovered 

 by Miss Hollingshead (19286), which removes all doubt as to the 

 possibility of parthenogenetic development of the egg in Crepis. 



Essentially different conditions have been disclosed by Belling 

 and Blakeslee (1922) in triploid Daturas. The majority of the 

 progeny of triploids consists of simple and double trisomies together 

 with diploids, the latter being present only in the amount of about 

 one-third of the total number of plants, and triploid plants do not 

 occur at all. As for the other expected combinations as well as the 

 higher grades of polyploidy (excepting tetraploidy), they were not 

 observed in the triploid progenies in Datura at all. 



In triploid Oenothera {Lamarkiana var. semigigas) according to 

 van Overeem (1920) the formation of all possible chromosomal com- 

 binations has been observed in ratios approximating those expected 

 from the binomial distribution. 



In triploid tomatoes according to J. W. Lesley (1928) only single, 

 double, and triple trisomies occur, altogether amounting to about 

 85 per cent of the progeny; the remaining 15 per cent consisting of 

 normal diploid plants. No tetraploids or higher grades of polyploidy 

 were observed. 



In other Crepis species, as shown above, the conditions are differ- 

 ent from those eJcisting in C. capillaris. In C. tectorum triploids 

 behave like those of Oenothera; in C. dioscoridis they produce few 

 trisomies and few triploids, the great majority of the offspring being 

 normal diploid plants. 



It is clear, therefore, that triploid representatives of different 

 species, even though closely related, may differ strikingly in the 

 types of progeny which they produce. 



As respects the biological importance of triploidy, attention should 

 be drawn first to the manifold instances of chromosomal variation 

 which are known to occur in the progeny of triploid plants. As has 

 been shown above, in addition to tetraploids, which are known to 

 occur in a number of other species, pentaploid and even heptaploid 

 plants are produced in the progeny of triploid plants of C. capillaris. 

 Triploidy represents, therefore, the initial step of the accumulation 

 of the chromatin material ; how far this process can go is not yet 

 known, but there is some evidence suggesting the possibility of far 

 higher grades of polyploidy than those which have been found to date. 

 Moreover, the tendency of triploids to produce polyploid interspecific 



