120 VEGETABLE PHYSIOLOGY 



the surrounding medium, such as sometimes rapidly 

 supervenes on the emergence of a shoot from a tuber or 

 a fleshy root. We find the seed contains in some part or 

 other of its substance, sometimes even in the embryo itself, 

 examples of great classes of food-stuffs which are the same 

 as those on which animal protoplasm is nourished, and 

 whose presence renders seeds such valuable material for 

 animal consumption. As these disappear during the 

 development of the young plant, which thus evidently 

 grows at their expense, we cannot doubt that they form 

 its food, and that vegetable protoplasm is essentially 

 identical with animal, at any rate so far as its methods of 

 nutrition are concerned. Proteins, carbohydrates, fats or 

 oils, together often with certain other bodies which are 

 less widely distributed, are the materials which, in various 

 forms, are met with. 



If we study the protoplasm of a living, active, vegetable 

 cell, and treat it with appropriate solvents, we can extract 

 representatives of these, or of some of them, from its 

 substance, in the interior of which they are held some- 

 times in solid amorphous form, sometimes in fine sus- 

 pension or in actual solution. The nutrition of the 

 protoplasm can only take place when these substances are 

 brought into the most intimate relations with it ; from 

 them, no doubt, in ways not yet discovered, it builds itself 

 up, and by its own decompositions it reproduces many of 

 them. The details, however, of the interchange of matter 

 between the living substance and its food, the way in 

 which the latter is transformed into the former, are points 

 about which almost everything essential remains still to be 

 discovered. 



But while we recognise that the ultimate nutrition of 

 protoplasm is dependent upon its receiving a supply of 

 such materials, we are face to face with the fact that, with 

 a few exceptions, the consideration of which may be 

 deferred, they are not furnished at all from the environ- 

 ment to the ordinary green plant, and often only partially 



