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. 
