1915] LOEB—REGEN ERATION 267 
conducting. vessels should be possible only if a certain minimum 
amount of water is contained in the conducting cells or vessels. 
The buds of an isolated node nearer the base of the stem may 
grow out if suspended in moist air, probably because such a piece 
does not dry out so easily. 
The following experiment rarely fails. If we suspend:a piece of 
stem consisting of several nodes and stripped of all leaves in moist 
air (fig. 33), the two most apical buds (b) will grow out. Their 
growth, which is usually slow, is greatly accelerated if we leave 
one leaf (or more) on the stem (6 in fig. 34). In two weeks the 
growth of the apical buds (8) in fig. 33, which had no leaves, was 
very slight, while it was strong in the stem (fig. 34) in which one 
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26 
25 29 
27 
Fics. 25-29 
leaf was left. Here we have the combined accelerating effect of 
stem and leaf upon the growth of the apical bud. 
Why is it that the apical bud grows out first ? Should this be 
connected with the anatomy of the conducting vessels, possibly 
in the way that the majority of these vessels go directly from the 
leaves to the growing point at the apex? 
Since the rapid growth of the bud on a stem inhibits or retards 
the growth of adventitious roots of the opposite leaf (fig. 2), it 
follows that the removal of the bud or the inhibition of its growth 
should favor the growth of adventitious roots in the notches of the 
leaf. This is indeed the case. If we suppress the growth of the two 
buds in an isolated node, we favor the growth of adventitious roots in 
the leaves if they are submersed in water (fig. 3). The same hap- 
pens if we split the node longitudinally (figs. 35, 36). The leaf 
