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 (intussus- 

 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} 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 WorJc. 



1 This term has recently been employed in a wider sense. 



