206 A TEXTBOOK OF BOTANY [Ch. IV, 13 



are utilized as hemp, or other cordage. Likewise the bark- 

 cork has uses dependent on its waterproof qualities. 



From the stores laid down by plants in their stems man 

 derives many foods, either directly through some vegetables 

 or indirectly through fodder plants. Most of his sugar 

 comes from the main stems of the Sugar Cane, and a little 

 from Maple, and some starch from Sago Palm, while special 

 storage stems, like potatoes, yield him specially rich harvest. 

 And likewise from stems he draws drugs, dyestuffs, tanning 

 substances, resins, rubber, and almost innumerable other 

 materials, having in the plant distinctive meanings which 

 involve properties happening to serve some human 

 purpose. 



Man's command over the resources of Nature rests not 

 alone upon his direct appropriation and use of materials 

 which plants happen to offer, but also upon his power to 

 multiply their quantity and improve their quality by culti- 

 vation. That part of cultivation which consists in conform- 

 ity to the plant's physiological peculiarities (page 94) is 

 comparatively simple with stems, involving no special hor- 

 ticultural or agricultural practice, doubtless because of the 

 relatively simple and mechanical part taken by stems in 

 the plant's economy. But the other phase of cultivation, 

 viz. improvement, which always depends on the utilization 

 of potentialities which the construction or composition of 

 the plant happens to offer, has some important applications 

 in stems, especially in connection with pruning and grafting. 



Pruning consists in the removal of some parts of a plant 

 for the benefit of the remainder. Its very possibility de- 

 pends on two leading facts. First, branches are practi- 

 cally all repetitions of one another, and hence are not in- 

 terdependent ; and accordingly any particular ones may be 

 removed without damage to the rest. Second, any injuries 

 made in living tissues of plants not only heal quickly, but 

 the bark gradually overgrows and permanently covers large 

 areas of dead tissues, as already described (page 122, Fig. 79). 



