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 1t 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 
