Adaptation to Environment. 



The adaptive modifications of the Cecropia having a 

 bearing solely on the problem of protection, are the thin 

 places through which the ants burrow an entrance, and the 

 never failing supply of food 

 at the bases of the petioles. 

 The hollow stem is found 

 in many plants, and is the 

 outcome of economy of ma- 

 terials in stem construction. 



203. Most Potent Environ- 

 mental Factors. Instances 

 showing adaptations to 

 special conditions might be 

 cited at great length, but 

 the few cases already given 

 suffice to show the power 

 of plants to meet such con- 

 ditions. It has already 

 been suggested that of all 

 the factors to which plants 

 must accommodate them- 

 selves, the water supply is 

 the most potent in molding 

 their form and visible con- 

 stitution. Indeed, so great 

 has this influence been that 

 those plants which have to guard against loss of water by 

 transpiration are very different in appearance from those 

 which find plenty of water at their disposal and may tran- 

 spire it unstintingly without danger to themselves. The for- 

 mer class of plants are termed xerophytes, or if growing in a 

 salty substratum they are termed halophytes (see paragraph 

 208^, while plants of the latter class are called hydrophytes. 



FIG. 167. 



A, longitudinal section through a portion 

 of a young stem of Cecropia adenopus, 

 showing partitions cut through by ants ; 

 B, apex of a young stem of Cecropia, 

 showing at a a thin place through which 

 the ants cut a way to the hollow inte- 

 rior. About one-half natural size. After 



SCHIMPER. 



