%, _—*) Y +. . Lo a —_ 4 
= a Rt RO Ta = Ae 
\ , 7 7 
Wee | : ¥ he Life of the Plant. : 
4 
| 175 
The experiments of Hanstein were the first: to prove this point. 
From the cut branches of various dicotyledonous plants he removed, 
above the cut surface, a circular piece of bark, and then placed the 
branch in water. The result was that in those species which possess no 
isolated vascular bundles, no cambium cells, and no sieve-tubes in the 
medullary sheath, no roots sprang from below the place from which the 
bark had been removed, or at least very few in proportion to the size of 
the piece of bark below; while above that part a large number of strong 
roots were formed (Fig. 348). In those plants, on the other hand, like 
Mirabilis Falapa and Amaranthus 
sanguineus, which have isolated 
vascular bundles in the pith, or, 
like Merium Oleander and Solamum 
Dulcamara, cambium-bundles or 
sieve-tubes, an abundance of roots 
were formed even below the part 
where the bark had been re- 
moved. The conclusion is un- 
avoidable that substances essential 
to nutrition are conducted only 
through the elongated cambium- 
or sieve-tube cells. In these cell- 
bundles, however, non-nitrogenous 
substances occur only exception- 
ally, that is only at periods when 
large quantities must be trans- 
ported in a short time; and in 
many plants they are never found : 
there. The conclusion may hence yy¢, 348.—A cutting from which a ring of 
be drawn that other groups of cells bark has been removed placed in water ; 
besides the elongated ones also ae irae seas aoe 
take part in the ‘transport of the 
assimilated sap ; and these are most probably certain groups of paren- 
chymatous cells which are distinguished by containing very fine-grained 
starch, and which can be recognised at once by this. 
It follows from what has been said that the old view of an ascending 
sap in the spring and a descending current in the autumn, must be 
modified ; that the sap certainly rises in the spring after the close of 
the winter’s period of rest; but that this ascending current continues 
through the whole period of growth, as does also the’ descending 
current ; and that, as need arises in the plant, horizontal currents also 
pass through its tissues. The old comparison between the circulation 
