NUTRITIOM AND GENESIS. 455 



the breakage quickly swell and burst iuto lateral shoots, 

 which often put forth secondary shoots : two generations of 

 agamic individuals arise where there probably would have 

 been none but for the local abundance of sap, no longer 

 drawn off. In like manner the abnormal awamogrenesis which 

 we have in proliferous flowers, is habitually accompanied by 

 a general luxuriance, implying an unusual plethora. 



No less conclusive is the evidence furnished by agamo- 

 genesis in animals. Sir John Dalyell, speaking of Hydra 

 tuba, whose peculiar metagenesis he was the first to point out, 

 says — " It is singular how much propagation is promoted by 

 abundant sustenance." This Polype goes on budding- out young 

 polypes from its sides, with a rapidity proportionate to the 

 supply of materials. So, too, is it with the agamic 



reproduction of the Aphis. As cited by Professor Huxley, 

 Kyber " states that he raised viviparous broods of both this 

 species (Aphis DianthiJ and A. Bosce for four consecutive 

 jears, without any intervention of males or oviparous females, 

 and that the energy of the power of agamic reproduction was 

 at the end of that period undiminished. Ihe rapidity of the 

 agamic prolification throughout the whole period was directly 

 proportional to the amount of warmth and food supplied." 



In these cases the relation is not appreciably complicated by 

 expenditure. The parent having reached its limit of growth, 

 the absorbed food goes to asexual multiplication : scarcely 

 any being deducted for the maintenance of parental lile. 



§ 354. The sexual multiplication of organisms under 

 changed conditions, undergoes variations conforming to a 

 parallel law. Cultivated plants and domesticated animals 

 yield us proof of this. 



Facts showing that in cultivated plants, sexual genesis in- 

 creases with nutrition, are obscured by facts showing that a 

 less rapid asexual genesis, and an incipient sexual genesis, ac- 

 company the fall from a high to a moderate nutrition. The 

 confounding of these two relations has led to mistaken infer- 



