22 WONDERS OF PLANT LIFE 



comes in its composition. Exposed to the magical 

 influence of the sun and air, the fluid is completely 

 elaborated. By a process which is not fully under- 

 stood the inorganic material taken up by the plant 

 from the soil is changed in such a way that it 

 can be assimilated by the tissues of the vegetable. 

 The sap is now very much altered in its con- 

 sistency. A large proportion of water has been 

 evaporated, and the fluid is thick and rich in 

 nutrient matter. Moreover, it will have acquired 

 certain peculiar properties in the case of the 

 Oak, for instance, these being of an astringent 

 nature. The course which the sap now pursues 

 will take it along the under side of the leaves, 

 through the new tissue, and so back to the roots 

 again. 



All the summer long the leaf lives a life of 

 intense activity, manufacturing a store of food 

 material which will be put aside in various parts 

 of the plant. With the coming of the autumn, 

 however, the vitality of the leaf steadily declines, 

 the sap movements become very slight, and the 

 time has come for the organ to be separated from 

 the tree. So far-seeing is Nature, that the leaf 

 is scarcely developed ere preparations are com- 

 menced for the severance of it from the twig. 

 Quite early in the history of the leaf at the point 



