224 



THE BEHAVIOUR OF POLYPLOIDS 



III. Drosophila (eye-facets) (Bridges, 1925 b). N.B. — The triploid 

 is an unrelated individual. 



WTien these observations are compared with similar observations 

 of diploid and polyploid forms of remote relationship, whether 

 species or varieties, various kinds of difference are found, which 

 may be classified under three heads. 



1. Many polyploid wild species and cultivated forms have the 

 same proportionate increase in size as is found in critical experiments, 

 and it may then be inferred that little change has taken place in the 

 polyploid since its origin. This conclusion is particularly obvious 

 because wild species of this kind are found to be propagated 

 vegetatively or " semi-vegetatively " {e.g., Vallisneria gigantea, 

 Jorgensen, 1927 a ; Caninae roses), and cultivated forms have been 

 subject to human selection in favour of size since their origin 

 [e.g., Triticum species, Sax, 1922 ; Petunia, Dermen, 1931). 



2. Certain polyploid species and races are no bigger, or are even 

 smaller, than their diploid relatives, yet in certain structures, such 

 as pollen grains, they preserve what must be supposed to be their 

 initial gigantism. This is true of the Cinnamomeae roses, where the 

 polyploid species are actually of smaller growth than the diploid 



Table 36 

 Linear Measurements of Cells in Polyploid Derivatives (in microns) 



6x. 



Petunia vars., pollen grains 

 Triticum species, pollen grains . 

 Rosa (sect. Cinnamomeae), pollen 

 mother-cells .... 



Primula obconica vars., pollen grains 

 Allium species, pollen grains 



55-3 



lO'O 



