The Aneuploids 353 



crossing between tetraploicls and diploids and between tiiploids and 

 dijiloicis were carried out, combinations could be extended to XYY, 

 XXX}', XXXry, XXXX)'. obviously, a great range may be pro- 

 duced. Everyone agrees that the Y chromosome is a determiner for 

 maleness because the j^resence ol this chromosome once or twice clearly 

 imjircsses its influence on the j^lant. Only when four X chromosomes 

 are opposing the one }' does the flower change to a hermaphrodite. 

 This tendency begins to show slightly among the XXXF type. The 

 XY and ATT are male without exception. ''•' 



The I^anish"*-^ and American''"- polyploids differed with regard to 

 the possible iniluence of autosomes and the role of the X chromosoine 

 as a female determiner. Some of the differences may be due to sources 

 of diploid plants and some difference to method as well as interpreta- 

 tion. Two critical j^apers must be studied if one wishes to weigh the 

 evidence: one by \Varmke.'^-' and another by ^\^estergaard.■■'•"' 



Cytologically the Y chromosome can be distinguished from the 

 smaller X. In turn, the X is larger than any autosomes. This feature 

 is highh desirable because certain problems woidd be difficult to 

 interjjret otherwise. The hybrid generation between tetraploid XXXX 

 and tetraploid XX}'}' throws 1 female to 12 males. The diploid sex 

 ratios are 1:1. Looking at the chromosomes, it can be seen that most 

 males are XXX}" (89 per cent) and only a few XX}'}' (4 per cent). 

 The association between XT and Y-Y is more frequent than between 

 X-}' and X-}'. A high proportion of gametes were X}' and the XX 

 and }'}' classes were low. If a male with chromosomes XXX}' was 

 crossed \vith a female XXXX. the offsjjring showed 50-50 male: female 

 ratios. Similar results were obtained with Acuida lamariscina (Nutt.) 

 \\ood,-'-^ and for Mehmdrnim dioecum var. alhuiii described above. •''^ 



In nature, the excess 4;/ males that are XXX}' instead of XXYY 

 would iertilize a large majority of the 4/7 females XXXX; hence, equal 

 populations of males and females at the tetraploid level could be 

 expected. From an evolutionary standjioint tetraploids differing on 

 the basis of X and }' determining maleness and femaleness could be 

 established much the same as a diploid species. A tetraploid race of 

 Ritinex acetosa has not been demonstrated as a stabilized dioecious 

 type.''^ 



Autotctraploid hemj) gave an excess of females in the second 

 generation follo^ving jjolyploidy.-'^ This was a reversal over the dip- 

 loid male-female proportions. Less cytological attention has been 

 given to this species. 



Polvjjloidy provides a method for deciding whether the male or 

 female is heterogametic. that is. carrying the X'}'. A test was made 

 for Silene otites since cvtological methods did not give a solution in 

 this case."'"' Polyploid plants would become XXXX and XX}'}^ but 



