80 PLANT-ANIMALS [OH. 



produced. The liberated energy serves for the per- 

 formance of the work which the living plant must do, 

 and also, converted into heat, contributes to maintain 

 the temperature of the plant's tissues at a proper 

 level. The surplus of carbohydrate and of protein 

 not used for constructive or respiratory purposes the 

 plant puts by for future use. The starch, oil and 

 nitrogenous substances contained in seeds, tubers, 

 and other storage-organs of plants represent this 

 reserve food-material. 



The power possessed by the green plant of manu- 

 facturing food-materials in excess of its immediate 

 needs is the lever which makes the whole world of 

 animal life to move. For the animal has no such 

 synthetic powers, and yet it requires the same food- 

 substances as the plant. Hence it is constrained to 

 take them from the plant. The aphorism "all flesh 

 is grass" is no mere figure of speech, but a terse 

 statement of truth. 



Though the foregoing facts are, of course, the 

 commonplaces of plant-physiology, yet they require 

 mention here, for it follows from them that, if C. ros- 

 coffensis does not take in solid food, it must either 

 absorb it in solution or manufacture food for itself. 

 Since the plant-animals not only live very well but also 

 increase and multiply in pure sea-water, and since pure 

 sea-water contains but the merest traces of any organic 

 substances which might serve them as food, we are 



