2 STRUCTURAL BOTANY 



respects the stem on which they grow. Later on 

 the flowers appear, borne on the upper part of the 

 stem and its branches, above the leaves. These 

 flowers, when they wither, give place to the fruits or 

 seed-vessels, and in these the seeds themselves are 

 ripened, which, when sown, will produce a new genera- 

 tion of wallflowers for next year. 



Now a plant, like all living things, is made up of 

 organs ; thus a leaf, a stem, a, root, or a flower is not 

 merely a part of the plant, but it is a part which does 

 some definite work for the good of the whole. The 

 highest or most perfect plants are those in which the 

 division of labour is most complete, in which the 

 principle of setting apart a distinct organ for each 

 distinct kind of work is most thoroughly carried out. 

 The Wallflower is an example of a very highly 

 organised plant. Later on we shall make the ac- 

 quaintance of plants in which there is little or no 

 division of labour in which, that is, the organs are 

 not distinct, or at least not evidently so. 



The work which an organ has to do is called its 

 function. In the Wallflower, as in the higher plants 

 generally, the root has two manifest functions : it has 

 to hold the plant firmly in the ground, and also to 

 take up food from the ground. The leaves have for 

 their chief office the absorption of food from the air ; 

 we shall soon find that a green plant obtains quite half 

 its food from this source. The stem has to conduct 

 the food, which the root and the leaves absorb, to other 

 parts of the plant, and it also has to support the 

 leaves in such a position that they may best be 



