6 THE FLOWERING PLANT. 
the breaking-down of the molecule. The instability of organic 
matter is due, not only to its complexity, but also to the presence 
of nitrogen as a component. This element does not readily com- 
bine with other elements, and the union, when effected, is a very 
weak one. The continual wasting of organisms must be made up 
for by the taking in of food from the exterior, which is built up 
into new protoplasm. All the protoplasmic parts of an organism 
are continually breaking down, and new molecules are, therefore, 
formed in all parts of the body. In brief, an organism undergoes 
constant waste and as constant renewal. 
(4.) If more food is taken in than is necessary to make up for 
waste, growth may result to a certain extent, and this is effected 
by formation of new molecules in all parts of the body (¢ntussus- 
ception). A plant or animal is, then, only constant as regards 
form, and not as regards the substance of which it is composed. 
This has been illustrated by comparison with a whirlpool, which 
may remain for a long time constant in shape, though new par- 
ticles of water are constantly entering it to replace those passing 
out. 
Inorganic matter does not undergo the constant breaking-down 
and renewal just described, and though it may exhibit a sort of 
growth, as seen in a crystal or a stalactite, this is not by intussus- 
ception, but by the addition of new layers to the outside (accretion). 
Thus the inner part of such a growing body is always older than 
the outer. Further, there is no fixed limit to this kind of growth, 
provided the external conditions are favourable. 
(5.) Lastly, organisms have what may be called a definite life- 
history.1 They come into existence, carry on certain functions, 
attain a maximum size, and lastly die, when their bodies break 
down into the simpler compounds from which they were originally 
derived. 
Having defined Botany and indicated the boundary-lines which 
mark off organisms from inorganic matter and plants from ani- 
mals, the importance of practical work must next be insisted on. 
The great use of all branches of Natural Science is to teach the 
habit of accurate and careful observation, and afterwards to build 
up theories on the facts thus obtained. Botany is extremely well 
suited to beginners in science, since abundant material is easily 
obtainable, and the instruments necessary in the early stages are 
comparatively few. Details will be found in the Appendix on 
Practical Work. 
1 This term has recently been employed in a wider sense. 
