206 INBEEEDING AND OUTBEEEDING 



which have resorted to vegetative propagation or par- 

 thenogenesis? Even self-fertilization, which is the rule 

 with many plants, nullifies the advantages which were re- 

 sponsible for its development. As far as there is signifi- 

 cance in amphimixis in inducing variability, continuous 

 self-fertilization must for the most part be left out of 

 consideration. "Weismann ^^^ states the problem : 



If amphimixis has been abandoned in the course of phylogeny by 

 isolated groups of organisms, this has happened beoause other advan- 

 tages accrued to them in consequence, which gave them greater security 

 in the struggle for existence ; but it must be admitted that they thereby 

 lost their perfect power of adaptation, and that they have thus bartered 

 their future for the temporary securing of their existence. 



Let us see what it is for which these organisms ^ * barter 

 their future.'' According to the view of heterosis out- 

 lined previously, there is no advantage in the hetero- 

 zygous state in itself, but on account of linkage it is 

 difficult to obtain all the more favorable characters which 

 exist in a species combined in one individual in a pure 

 breeding, homozygous condition. There is always the 

 possibility of obtaining such combinations, however, and 

 the resulting individuals are well fitted for survival 

 as long as the environment remains the same. If the pro- 

 duction of these favored few is accompanied by any 

 change which renders cross-fertilization difficult, and if 

 there is nothing to prevent them from resorting to self- 

 fertilization, parthenogenesis or vegetative means of 

 propagation, there is no obvious reason why the plants 

 should not undergo the change. They would possess the 

 most efficient means of multiplication and would doubtless 

 be fitted for survival through long periods of time. They 

 would not be flexible, however, and if the environment 



