MOVEMENTS OF NUTRIENT MATTERS. 341 
vessels, though they do not commonly penetrate the spiral 
ducts, but ascend in the sieve-cells of the cambium.* 
The rapid supply of water to the foliage of a plant, 
either from the roots or from a vessel in which the cut 
stem is immersed, goes on when the cellular tissues of the 
bark and pith are removed or interrupted, but is at once 
checked by severing the vascular bundles. 
The proper motion of the nutritive matters in the plant 
—of the salts dissolved from the soil and of the organic 
principles compounded from carbonic acid, water, and 
nitric acid or ammonia in the leaves—is one of slow dif- 
Susion mostly through the walls of imperforate cells, and 
goes on in all directions. New growth is the formation 
and expansion of new cells into which nutritive substances 
_are imbibed, but not poured through’ visible passages. 
When closed cells are converted into ducts or visibly com- 
municate with each other by pores, their expansion has 
ceased. Henceforth they merely become thickened by in- 
terior deposition. 
Movements of Nutrient Matters in the Bark or Rind. 
—The ancient observation of what ordinarily ensues when 
a ring of bark is removed from the stem of an exogenous 
tree, led to the erroneous assumption of a formal down- 
ward current of “ elaborated ” sap in the bark. When a 
cutting from one of our common trees is girdled at its 
middle and then placed in circumstances favorable for 
growth, as in moist, warm air, with its lower extremity in- 
water, roots form chiefly at the edge of the bark just 
above the removed ring. The twisting, or half-breaking, 
as well as ringing of a layer, promotes the development 
of roots. Latent buds are often called forth on the stems 
of fruit ‘trees, and branches grow more vigorously, by 
making a transverse incision through the bark just below 
* As in Unger's experiment of placing a hyacinth in the juice of the poke- 
weed (Phytolacca,) or in Hallier’s observations on cuttings dipped in cherry-j Juice, 
(V3. St., TX, p. 1.) 
