116 



ADJUSTMENT TO ENVIRONMENT 



chance of maturing seed. From considerations of this 

 sort it is plain that the tree does react to climatic condi- 

 tions in such a way that the reproductive processes are 

 properly regulated. When plants are taken from one re- 

 gion to another it not infrequently happens that they 

 grow vigorously but fail to flower or to set seed. Some 

 of the necessary stimuli are wanting. The climate may 



Fio. 26. — A Rosette of Leaves so arranged as to expose each 

 leaf lus fully as j>os.sihlc to light. Although not .so obvious, the leaves 

 of mo-st plants are accurately placed to take the l)est advantage of 

 the available liRht. 



be too wet or too dry, too hot or too cold, the light too 

 intense or too weak, or some characteristic of the soil 

 may be unsuitable. 



Lack of water stimulates reproduction in many kinds 

 of plants. Among the Algae are many which have two 

 methods of reproduction, a sexual and a non-sexual one 

 (Chap. XXVI). When water is fresh and abundant they 



