122 LIFE IN NATURE. 



some plants be incised, buds spring up from the cut 

 surface ; or a new hydra grows from a wound in its 

 parent : an artificial axil being made. Other circum- 

 stances, doubtless, are concerned in repair ; but the 

 general fact is a simple exhibition of the mechanical 

 direction of growth. The new material is accumu- 

 lated where the resistance to expansion is removed : 

 is it not deposited there rather than in other por- 

 tions of the body, because the resistance at that point 

 is the least ? We know that repair is effected at the 

 expense of the general nutrition of the body : and we 

 know, too, the effect of pressure in limiting it. At 

 least we may say this : that if this law of growth be 

 true, then it is certain (other circumstances being the 

 same) that wounds must be repaired. 



Dr. Macvicar has adduced very striking arguments 

 to show that the natural forces, regarded in their most 

 general aspect, tend to the production of the sphere 

 the most perfect form and that the phenomena of 

 organic development are, to a very large extent, in- 

 terpretable from this point of view. " It is precisely 

 those forms which geometry shows to be most highly 

 endowed, that natural bodies tend to emulate in their 



