Autopolyploids and Evolution 453 



ranging from one to five (Fig. 131). In fifteen different meta- 

 phase figures of the first meiotic division there were fourteen 

 different combinations. The average numbers per cell were: 

 univalents, 1.73; bivalents, 3.60; trivalents, 2.60; quadrivalents, 

 1.40; and quinquevalents, 2.67. As is to be expected according 



-tt^ li f| M V ^ftl U 



Fig. 131. Meiotic configurations of a pentaploid Dactylis. Present in 

 the cell are 1 hexavalent, 4 quinquevalents, 1 quadrivalent, 2 bivalents, 

 and 2 univalents. (Redrawn from Miintzing in Hereditas.) 



to the behavior of chiasmata, there were fewer quinquevalents 

 in the pentaploid than there were quadrivalents in related tetra- 

 ploids, and in turn there were fewer quadrivalents in these tetra- 

 ploids than there were trivalents in related triploids. 



Autopolyploids and Evolution 



Because of the generally greater size and vigor of autopoly- 

 ploids, the possibility that they might have played an important 

 role in evolution must be considered. Because of their sterility, 

 triploids are of little importance unless they reproduce vegeta- 

 tively. As a matter of fact, however, neither triploids nor tetra- 

 ploids represent anything strikingly new in most genera, for they 

 usually differ from the diploid stock merely in vigor and other 

 attributes of growth. This difference has been studied carefully 

 in Tradescantia. 



Both T. occidentalis and T. canaliculata contain diploids and 

 tetraploids, and in both species the two types resemble one an- 

 other so completely that not only are they not classified as sepa- 

 rate subspecies or varieties but they cannot even be classed as 

 diploids or tetraploids on the basis of their external appearance. 

 When they have been classified by cytological examinations, it is 

 easy to see that the tetraploids are definitely larger and have 

 longer blooming seasons. Because of their greater vigor, they 

 have greater ability to colonize. Each species apparently arose 



