104 LIFE IN NATUKE. 



which produce growth ; as, for instance, to a local 

 decomposition generating a greater energy of vital 

 action in that part, according to the law explained 

 in the previous chapters. In these cases, the local 

 growth resembles the increased development of 

 plants on the side which receives most light. And 

 the causes of the greater energy of growth in one 

 part than another, may be often traced back several 

 steps ; as when an increased pressure produces a 

 local decomposition, and this gives rise again to a 

 new organizing action. 



Thus some apparent exceptions to the law of 

 growth in the direction of least resistance receive 

 an explanation. As, for example, that the root 

 extends beneath the soil, and overcomes the resist- 

 ance of the earth. The answer to this objection 

 is, first, that the soft cellular condition of the 

 growing radicles forbids the idea that the roots 

 force themselves into the ground ; and secondly, that 

 their growth is accounted for by the presence in 

 the soil of the agencies which produce growth. In 

 truth, the formation of the root affords a beautiful 

 illustration of the law of least resistance, for it 



