Autotriploids 



441 



plant was somewhat larger than normal; fertility was low 

 and the pollen was largely bad. Triploids are usually highly 

 sterile, as a matter of fact, and are not self-perpetuating sexually 

 in spite of their greater vigor. However, if they can reproduce 

 asexually, as by rhizomes, they may establish permanent clones 

 that have a decided advantage in competition with their diploid 

 relatives. 



Fig. 125. Photomicrographs of first metaphase in a triploid Tradescantia 

 showing trivalent configurations. At left, five Y-shaped trivalents and a 

 ring-and-rod (towards bottom of picture). At right, two chains of three 

 chromosomes are clearly visible. In the upper left corner of the picture at 

 the left are two small centric fragments. 



If an autotriploid can be regarded as merely an organism that 

 is trisomic for all its chromosomes, it should form the same 

 kinds of meiotic configurations for all its chromosomes that the 

 primary trisomic does for its single triplicated chromosome. 

 Sometimes it should have only trivalents, at other times it should 

 have some bivalents and univalents in place of some trivalents. 

 Perhaps, very rarely, it should have only bivalents and univa- 

 lents, although this would hardly be likely to occur in an auto- 

 triploid unless some special circumstances were present. The 

 trivalents should exhibit the same rods, Y's, and other configura- 

 tions found in Fig. 114, although the type in which all three 

 chromosomes are joined at one end is rare. Plants with such 

 configurations have often been found (Fig. 125). A good ex- 

 ample is an autotriploid of Tradescantia hracteata, which was 



