UNBALANCE AND STERILITY 321 



Table 50 

 Transmission of Extra Chromosomes of Trisomies to their Progeny* 



* 50 per cent, expected : the reduction is chiefly due to elimination of 

 abnormal gametes, but partly also to elimination of abnormal zygotes. 



t Pentasomic allo-tetraploid. 



X Trisomic tetraploid : the high transmission oi2x—i eggs is due to frequent 

 loss of the unpaired chromosome at meiosis so that more 2;«r— i eggs than 2.x 

 are formed. No 4;^; — 2 seedlings appear. 



Table 51 

 Pollen Abortion in Datura (after Blakeslee and Cartledge, 1926). 



Type of plant . 

 Percentage bad pollen 



4X 



5 



Notes. — (i) There are no monosomies in the progeny of haploids, therefore 

 X — 1 eggs and pollen or 2;^; — i zygotes are non-viable. 



(ii) The primary trisomies with the poorest pollen are not those with the 

 poorest growth and lowest frequency of appearance in progeny of triploids. 

 Therefore the disadvantageous effect of the extra chromosome is specific in 

 regard to time of action. 



(iii) The pollen abortion is higher in the tetraploid than in the diploid 

 [cf. Table 28). 



R.A. CYTOLOGY. 



11 



