CHAP. VIII Vitality 133 



the conclusion that the substance of the network is of a 

 different character from the substance filling up the meshes. 

 Similar analysis shows that at times the bars or films of the 

 network are not homogeneous, but composed of different 

 kinds of stuff ; yet even in these cases it is difficult, if not im- 

 possible, to recognise any definite relation of the components 

 to each other such as might deserve the name of structure." 

 Plainly there is not much light to be got by further investi- 

 gations in this direction. Ordinary chemical analysis, too, 

 is of little avail ; for how can we say what parts of the 

 mass are alive, even if we could separate part from part ? Is 

 it only the meshwork that is really living matter, or are the 

 granules part of it, or are the fluid contents the chiefly vital 

 substance ? 



Let us turn now to the activities of the living stuff, and 

 see what we can learn from them. We have already spoken 

 of one of the activities of living matter, especially of plant 

 protoplasm, that of surrounding itself with a wall. Now we 

 might at first be inclined to suppose that the wall was simply 

 due to a hardening and drying of the soft substance at those 

 places where it touched the air. It is possible that that may 

 have been the stimulus which caused, as a reaction, the 

 wall-making at the dawn of life, and which may still have 

 some connection with it ; but what we have to take note of 

 is the fact that the walls, as they are made by the higher 

 plants, have always a definite structure and chemical nature. 



If we examine the cells of the leaves of a plant growing 

 in the sunlight, we find the green colouring matter to be 

 generally collected in little rounded masses. Looking more 

 closely, we find it to be the fluid which fills the meshwork 

 of the masses. At certain points in the meshwork we find 

 minute masses of starch constantly being formed. They seem 

 to pass along the strands and collect in the centre of the net- 

 work, until quite a large mass of starch is accumulated there. 

 If we examine the plant at night, some time after darkness 

 has set in, we find no traces of starch in the cells of the 

 leaves. There is evidence that the starch has been trans- 

 formed into sugar, and can then, by osmotic and perhaps 

 by other processes, be removed from the leaves, and 



