386 University of California Publications in Agricultural Sciences [Vol. 2 



of somatic duplication before reduction they will be of three different 

 kinds: viz., (1) both satellites large; (2) both satellites small: and 

 (3) unequal satellites. Finally, if duplication of a reduced nucleus 

 has taken place, the gametes will be of two different kinds either with 

 both satellites small or with both satellites large. If the original 

 l)lant with unequal satellites is crossed with a plant having equal 

 satellites one can easily get direct evidence as to the manner of origin 

 of the occasional triploids. If among the triploids there are plants 

 with three equal satellites, the cause of triploidy cannot be due to 

 non-reduction, but if there are no plants of that sort then triploidy 

 must be due to non-reduction. Taking special precautions one can 

 even find out w^hether duplication took place before or after reduc- 

 tion. Special experiments in this direction are in progress. 



No matter what the manner of origin of triploidy may be, it may 

 undoubtedly play a considerable role in the genetic behavior of the 

 species involved. Besides the well-known peculiarities of Mendelian 

 inheritance caused by new^ trisomic and polyploid chromosome com- 

 binations, attention should be drawn here to some other consequences 

 of triploidy. 



In table 3 (p. 381) it is shown that 92.7 per cent of the entire 

 progeny of triploid plants of C. capillaris consists of normal diploid 

 plants (63.9 per cent) and triploid plants (28.8 per cent) ; and the 

 remaining 7.3 per cent of higher grades of polyploidy (4.0 per cent), 

 various trisomies (3.0 per cent), and triploid tetrasomics (0.3 per 

 cent). 



From the same table it may be seen that these figures are not in 

 agreement with those expected from the binomial distribution of the 

 extra haploid complex (see table 3, column "expected"), but are in 

 conflict with it in several respects. Thus instead of the expected 

 75 per cent of trisomies only 3 per cent were actually obtained; and 

 instead of 25 per cent of diploids and triploids, as a matter of fact 

 there are 92.7 per cent. In order to explain the deficiency of trisomies 

 the percentage of aborted seeds was determined under the suppo- 

 sition that they should represent elimination of eggs bearing 1 or 2 

 extra chromosomes. As may be seen from table 1 the triploid plants 

 set on the average only 21.8 per cent of good seeds; the lack of 72 

 per cent of the expected trisomies is therefore in full agreement with 

 the ob.served reduction in the number of good seeds. It is further 

 very probable that the lack of trisomies may be due to partial zygotic 

 sterility arising from disturbances which in the majority of instances 



