344 HOW CROPS GROW. 



ring of bark is removed from a cutting, rocts often appear 

 below the incision, though in less number, and .the new 

 growth at the edges of a wound on the trunk of a tree, 

 though most copious above, is still decided below goes 

 on, in fact, all around the gash. 



Both the cell-tissue and the vascular thus admit of the 

 transport of the nutritive matters downwards. In the 

 former, the carbohydrates starch, sugar, inulin the fats, 

 and acids, chiefly occur and move. In the large ducts, air is 

 contained, except when by vigorous root-action the stem 

 is surcharged with water. In the sieve-ducts (cambium) 

 are found the albuminoids, though not unmixed with car 

 bohydrates. If a tree have a deep gash cut into its stem, 

 (but not reaching to the colored heart-wood,) growth is 

 not suppressed on either side of the cut, but the nutritive 

 matters of all kinds pass out of a vertical direction 

 around the incision, to nourish the new wood above and 

 below. Girdling a tree is not fatal, if done in the spring 

 or early summer when growth is rapid, provided that the 

 younsj cells, which form externally, are protected from 

 dryness and other destructive influences. An artificial 

 bark, i. e., a covering of cloth or clay to keep the exposed 

 wood moist and away from air, saves the tree until the 

 wound heals over.* In these cases it is obvious that the 

 substances which commonly preponderate in the sieve- 

 ducts must pass through the cell-tissue in order to reach 

 the p^int where they nourish the growing organs. 



Evidence that nutrient matters also pass upwards in 

 the bark is furnished, not only by tracing the course of 

 colored liquids in the stem, but also by the fact that undo 

 veloped buds perish in most cases when the stem is gir 

 dled between them and active leaves. In the exceptions 

 to this rule, the vascular bundles penetrate the pith, and 



* If the freehly exposed wood he rubbed or wiped with a clolh, whereby tho 

 aioist wmtlai layer (o f cells containing nuclei aud capable of IT iltiplying) is re 

 moved, no growth can occur. Ratzeburg. 



