18 THE NATURE-STUDY OF PLANTS 
surroundings we shall very soon be aware of the third, 
which is Growth. 
Ill. GrowTH 
All healthy young things grow, and it is easy 
enough to understand that they grow because when 
they are born the body is not fully developed, some 
of its organs are not yet fully formed, and it has, as we 
say, to grow up. 
I said in the first chapter that it is often very 
hard to discover how things are done ; but if we want 
to get some little idea of how we grow we can hardly 
do better than consider the lilies of the field, for we 
both of us do so in the same way. 
Let us look once more at a section of a root or a 
stem. If we examine it with a lens we shall see that 
it is divided into innumerable little compartments, 
each of which, with its contents, is called a cell. Now, 
it is common knowledge that in course of time the 
green spring shoot of a tree becomes first a brown 
twig and ultimately a thick branch or bough, and one 
would like to know exactly how all this is managed. 
Confining ourselves to the increase in size, it will 
perhaps occur to us that it might be brought about 
in more ways than one; the cells, for example, might 
go on growing larger indefinitely, or they might 
become more numerous after attaining a certain 
size, and if we compare a section from a young thin 
stem with another from an older and thicker one we 
shall find that the latter is the method adopted. 
Growth, then, is effected by an increase of the cells, 
not in size but in number. 
That does not tell us much, it does not explain in 
