476 LAWS OP MULTIPLICATION. 



the breakage quickly swell and burst into 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 agamogenesis 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, and of the period before strobilization commences, 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 Dianthi) and A. Rosce for four con- 

 secutive years, without any intervention of males or ovi- 

 parous females, and that the energy of the power of agamic 

 reproduction was at the end of that period undiminished. 

 The rapidity of the agamic proliferation 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 

 life. 



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, 



