290 THE INDUCTIONS OF BIOLOGY. 



genetic multiplication, to obtain materials for growth better 

 than they would do did they not thus continually divide and 

 disperse in pursuit of it. The higher plants, having for 

 nutriment the carbonic acid of the air and certain mineral 

 components of the soil, show us modes of multiplication 

 adapted to the fullest utilization of these substances. A 

 herb with but little power of forming the woody fibre re- 

 quisite to make a stem that can support wide-spreading 

 branches, after producing a few sexless axes produces sexual 

 ones; and maintains its race better, by the consequent early 

 dispersion of seeds, than by a further production of sexless 

 axes. But a tree, able to lift its successive generations of 

 sexless axes high into the air, where each gets carbonic acid 

 and light almost as freely as if it grew by itself, may with 

 advantage go on budding-out sexless axes year after year; 

 since it thereby increases its subsequent power of budding- 

 out sexual axes. Meanwhile it may advantageously trans- 

 form into seed-bearers those axes which, in consequence of 

 their less direct access to materials absorbed by the roots, 

 are failing in their nutrition ; for it thus throws off from a 

 point at which sustenance is deficient, a migrating group of 

 germs that may find sustenance elsewhere. The hetero- 

 genesis displayed by animals of the Coelenterate type has 

 evidently a like utility. A polype, feeding on minute 

 annelids and crustaceans which, flitting through the water, 

 come in contact with its tentacles, and limited to that quan- 

 tity of prey which chance brings within its grasp, buds out 

 young polypes which, either as a colony or as dispersed in- 

 dividuals, spread their tentacles through a larger space of 

 water than the parent alone can; and by producing them, 

 the parent better insures the continuance of its species than 

 it would do if it went on slowly growing until its nutrition 

 was nearly balanced by its waste, and then multiplied by 

 gamogenesis. Similarly with the Aphis. Living on sap 

 sucked from tender shoots and leaves, and able thus to take 

 in but a very small quantity in a given time, this creature's 



