Self -Sterility 135 



are regarded merely as fluctuations or responses. Such 

 variations are not inherited, and therefore can be of no 

 phylogenetic significance; that is, of no value to the 

 future of the species. Our recent knowledge of the 

 factor hypothesis, however, indicates that many of these 

 variations are more than fluctuations. They may 

 represent germinal differences, such as varying "doses," 

 and such differences are inherited and may be of some 

 value therefore in the future of the species. 



It will be realized, however, that it is possible to 

 have a homozygous race. If a race were strictly 

 homozygous in respect to every heritable factor the 

 sex act would result in no more variation than would 

 asexual reproduction, provided of course our ideas of the 

 mechanism of inheritance in sexual plants are correct. 

 The fact is that a perfectly homozygous plant is probably 

 rare. Supposing, however, that it were common, we 

 would have to resort to some other mechanism than the 

 sex act to secure the desirable variation. If sex does 

 not secure variation what can ? 



The answer is cross-polUnation. Although races 

 were all homozygous, cross-pollination would make 

 possible the crossing of different races, which would 

 inevitably result in great variation in the progeny. 

 Even if homozygous races are few it is certainly true that 

 in any event cross-polUnation results in greater variation 

 than self-polUnation. This is the biological basis of 

 the many devices in plants to secure cross-pollination; 

 in fact, this is carried to such an extreme in many 

 cases that self-pollination is absolutely prevented. Sta- 

 mens and carpels may mature at different times; and 

 the great number of dioecious plants must all be 



