34 THE GROWTH OF THE TREES. 



the leaf that remain outward form the stigma. That the 

 flower is a charming device for the purpose of producing fruit 

 and seeds, we know well ; and even though it may not always 

 be beautiful there is usually attached to it some peculiar interest. 



While the tree is making this visible growth above ground, 

 we must not forget that under the soil its roots are busy branch- 

 ing and extending themselves that they may hold firmly the 

 tree in its upright position, and drain from the soil more nour- 

 ishment to supply its increased growth. The simple root that 

 first grows downward from the end of the embryo remains, in 

 many instances, for a long time the main root, (Plate VI.) and 

 from it sends off side branches ; more often, however, it soon 

 divides up into branches that in their turn again branch. As 

 has been mentioned, it is the fresh young roots that absorb the 

 nourishment from the soil. To aid them in so doing their sur- 

 faces are sometimes closely covered with root hairs. These 

 are simply elongations of the surface, or cells that are pro- 

 jected, and their thin coverings allow them greedily to imbibe 

 moisture into their tube-like interiors. It is from these well- 

 supplied young roots that the sap is drawn up to feed the 

 leaves and growing parts of the tree. 



This upward rise of the sap from the roots to the leaves is a 

 subject of much interest. It takes place principally through 

 the wood cells. And yet each one of these cells is a closed and 

 separate cavity ; they in no way open into each other as is gen- 

 erally supposed. By what means, then, we may ask, does the 

 sap pass through them. It is possible for it to do so because, 

 although there are no holes in the young cells, there are thin 

 places in their thick walls ; and the passage through is further 

 facilitated by the thin place in one cell connecting with the thin 

 place in the wall of the adjoining cell. That the leaves are 

 able to draw the contents of these cells up to them from the 

 roots, while seemingly most wonderful is by a natural law. 



We find that, whenever two fluids of different degrees of dens- 

 ity are separated from each other by a membranous partition, 



