956 HOW CROPS GROW. 
capable of feeding the plant from a dry soil, and hence 
the soil must be at first profusely watered; after a time, 
however, new roots are thrown out, which are adapted to 
the altered situation of the plant, and then the growth 
proceeds in the usual manner. 
The reverse experiment would seem to confirm this 
view. If a seedling that has grown for a short time only 
in the soil, so that its roots are but twice or thrice branch- 
ed, have these immersed in water, the roots already form- 
ed mostly or entirely perish in a short time. They indeed 
absorb water, and the plant is sustained by them, but im- 
mediately new roots grow from the crown with great ra- 
pidity, and tike the place of the original roots, which 
become disorganized and useless. It is, however, only the 
young and active rootlets, and those covered with hairs, 
which thus refuse to live in water. The older parts of the 
roots, which are destitute of fibrils and which have nearly 
ceased to be active in the work of absorption, are not af- 
fected by the change of circumstance. These facts, which 
are due to the researches of Dr. Sachs, ( Vs. Sé., 2, p. 135) 
would naturally lead to the conclusion that the absorbent 
surface of the root undergoes some structural change, or 
produces new roots with modified characters, in order to 
adapt itself to the medium in which it is placed. It 
would appear that when this adaptation proceeds rapidly, 
the plant is not permanently retarded in its growth by a 
gradual change in the character of the medium which 
surrounds its roots, as may happen in case of rice and 
marsh-plants, when the saturated soil in which they may 
be situated at one time, is slowly dried. Sudden changes 
of medium about the roots of plants slow to adapt them- 
selves, would be fatal to their existence. 
Nobbe has, however, carefully compared the roots of 
buckwheat, as developed in the soil, with those emitted in 
water, without being able to observe any structural differ 
eneea The facts detailed above admit of partial, if not 
ee en 
