368 HOW CROPS GROW. 
If a twig be cut from a tree in winter 
and be placed in a room having a summer 
temperature, the buds, before dormant, , 
shortly exhibit signs of growth, and if } 
the cut end be immersed in water, the ‘ 
buds will enlarge quite after the normal 
manner, as long as the nutrient matters 
of the twig last, or until the tissues at 
the cut begin todecay. It is the summer 
temperature which excites the chemical 
changes that result in growth. Water 
is needful to occupy the expanding and 
new-forming cells, and to be the vehicle 
for the translocation of nutrient matters 
from the wood to the buds. Water en- 
ters the cut stem by imbibition or capil- 
larity, not merely enough to replace loss 
by exhalation, but is sucked in by osmose 
acting in the growing cells. Under the 
same conditions as to temperature, the 
roots expand earlier and more rapidly 
than cuttings. Artificial pressure on the 
water which is presented to the latter, 
acts with an effect similar to that which 
the natural stress caused by the root- 
power exerts. This fact was demon- 
strated by Boehm (Siteungsberichte der ™ 
Wiener Akad., 1863) in an experiment 
which may be made as illustrated by the 
cut, fig. '70. A twig with buds is secured ° 
by means of a perforated cork into one 
end of a short, wide glass tube, which 
is closed below by another cork through 
which passes a narrow syphon-tube, B. 
The cut end of the twig is immersed in Fig. 70, 
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