440 Morpho genetic Factors 



Members of a polyploid series often differ in other respects than size. 

 There is a general tendency in tetraploids for organs to be relatively 

 shorter and wider than in diploids. This difference is well shown in the 

 series of capsules in Datura from In to An (Blakeslee, 1934). The 

 haploid has a slender capsule and becomes progressively flatter in the 

 upper members of the series. Fruits of tetraploid cucurbits produced by 

 colchicine were in every case changed toward a flatter, or at least a less 

 elongate, form. The leaves of tetraploid varieties of most plants show 

 the same shape changes in comparison with the diploid. Straub (1940) 

 observed that flower size changes in the same way, flowers from higher 

 members of a polyploid series being relatively wider. In Torenia the 

 position of the anthers with reference to the corolla is changed in the 

 octaploid. 



40 



60 ao ioo 



8 10 20 



OVARY DIAMETER mm 

 Fig. 19-11. Graph showing general relations between cell size and ovary size in de- 

 veloping fruits of diploid and tetraploid cucurbits. In early stages the 4N is larger in 

 both respects but after flowering the growth of the 2N is greater and at fruit ma- 

 turity (vertical bar) the two are essentially alike. (From Sinnott and Franklin.) 



This shape difference probably originates at the meristem itself. 

 Cross and Johnson found that in Vinca rosea the tetraploid apex was con- 

 siderably wider but no deeper and that the increase in size of its com- 

 ponent cells was also chiefly in width. Riidiger (1952) has shown that 

 in various plants the cells of the tetraploid are somewhat shorter and 

 wider than those of the diploid. Organ shape may thus be a reflection 

 of cell shape, though in other cases cell shape seems not to be markedly 

 different in An and 2n. Why there should be such a shape difference, 

 either in cell or organ, is not clear. Cell size alone is not enough to ac- 

 count for it, for there are large-celled races which do not differ in 

 shape from small-celled ones of the same species. 



Certain more general biological facts are related to polyploidy. Steb- 

 bins (1938), for example, has studied polyploidy in a large number of 

 woody and herbaceous genera and finds that polyploid series are more 



