THE STEM AND BRANCHES. 175 



we never said a word at the time about the means 

 by which the materials in question were carried 

 about and distributed to the various organs in 

 need of them. Nevertheless, a moment's con- 

 sideration will show you that new leaves and 

 shoots must necessarily be built up at the expense 

 of materials supplied by the older ones; that 

 flowers, fruits, and seeds must be constructed 

 from protoplasm handed over for their use by the 

 neighbouring foliage. Nay more; the root itself 

 grows and spreads; and the very tips of the 

 roots, which themselves of course can manufac- 

 ture nothing, must be supplied from above with 

 most active and discriminating protoplasm, to 

 guide their movements. Whence do they get it ? 

 From the factory in the foliage. Thus, from the 

 summit of the tallest tree down to the lowest 

 root that fastens it in the soil, there runs a com- 

 plex system of pipes and tubes for the special 

 conveyance of elaborated material ; and this sys- 

 tem supplies every growing part with the food- 

 stuff necessary for its particular growth, and 

 every living part with the food-stuff necessary 

 for maintaining its life and activity. An inter- 

 change of protoplasmic matter, starches, and 

 sugars, goes on continually through the entire 

 organism. 



This downward and outward stream of living 

 matter, carrying along with it live protoplasm 

 and other foods or manufactured materials, must 

 be carefully distinguished from the upward stream 

 of crude sap which rises from the roots to the 

 leaves and branches. The one contains only such 

 raw materials of life as are supplied by the soil — 

 namely, nitrogenous matter, water, and food- 

 salts ; the other contains the things eaten from 



