42 THE LIFE OF THE PLANT 



reveals the following substances : the wall, the proto- 

 plasm, the sap, and occasionally other bodies such as 

 drops or grains. 



So much for the microscope. Now let us return to 

 chemistry with its balance and reagents ; but this time 

 let us stop a little earlier in our analysis without reducing 

 the plant right down to its elements. We shall try to 

 separate out the different substances which enter into 

 the composition of the plant without destroying them, 

 dealing with them as they actually exist in the plant. 

 In a word let us study the proximate constituents of a 

 plant — I say proximate in contradistinction to the 

 ultimate constituents, which are the elements. 



Evidently it is impossible to study here all the 

 various substances which the vegetable world produces 

 — everything we find at our grocers' and chemists' 

 shops, at the carpenters' and the confectioners', in - 

 spinning factories and at dyeworks. We shall limit 

 ourselves to the commonest bodies, or rather groups of 

 bodies, without a study of which it is impossible to 

 understand vegetable life. 



Let us choose for an illustration some vegetable 

 organ, say grains of corn. Let us take them in a 

 powdered form, as flour. As we shall see in a moment, 

 flour represents a heterogeneous mixture of substances. 

 To separate them let us prepare a small lump of dough, 

 and wash it a long while with water, working and knead- 

 ing it with, our hands. At first the water runs off milky- 

 white in colour, but gradually it becomes quite clear. 

 We have now instead of dough a lump of something, 

 greyish-white in colour, sticky, and flexible like india- 

 rubber or leather. This is called gluten, and is that 

 constituent part of flour which makes dough sticky. 

 If, on the other hand, we let the water stand which ran 

 off during the washing we observe that it becomes quite 

 clear, while a very thin white sediment, quite soft to 

 the touch, forms at the bottom of the glass. This is 



