344 HOW CROPS GROW. 
ring of bark is removed from a cutting, roots 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- 
pony craigs. 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 
young 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 point 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 unde- 
veloped buds ish 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 freshly exposed wood be rubbed or wiped with a cloth, whereby the 
moist cambial layer (of cells containing nuclei and capable of multiplying) is re- 
moved, no growth can occur. Ratzeburg. Z 
