THE FOOD OF PLANTS 131 



plants. We cannot, therefore, speak of a differentiated 

 organ of digestion. 



Starting, then, with the intricacy of the metabolic pro- 

 cesses placed before us, and with their relations to each 

 other, we may begin the consideration of them in detail 

 with an inquiry into the preliminary absorption of the 

 materials from which the food is ultimately made. Even 

 here we meet with some complexity, as the ordinary green 

 plant shows marked differences in behaviour from its 

 parasitic relative and from the great class of Fungi, which 

 possess no chlorophyll. We have already pointed out that 

 the construction of food does not follow exactly the same 

 course in green plants and saprophytic fungi, the chief 

 point of difference being seen in connection with the carbo- 

 hydrates. It will be best to consider first the ordinary 

 terrestrial green plant, noticing in passing differences in 

 behaviour shown by aquatic and epiphytic forms. 



