LESSONS IN BOTANY. 189 



plant. Many plants are saprophytes or partly so, deriving their 

 food wholly or partly from decaying matters. 



The processes of assimilation and metabolism can only be car- 

 ried on within certain degrees of temperature; the limits vary with 

 different plants. In many plants these changes progress at tem- 

 peratures very little above freezing point, and in some plants 

 they are carried on freely at a temperature of from 110 to 120 

 F. Many of the subjects mentioned in this chapter will be more 

 fully discussed and illustrated in subsequent chapters. 



