790 FUNCTIONS OF THE ROOT.—ABSORPTION. 
Section 2. PHystioLoGy OF THE ORGANS OF NUTRITION. 
1. Or THE Root or Descenpinc Axis.—The offices per- — 
formed by the root are :—1. To fix the plant firmly in the earth or 
to the substance upon which it grows, or, in some aquatic plants, 
to float orsuspend it inthe water. 2. Toabsorb liquid food. 3. 
According to some authors, to excrete into the soil certain 
matters which are injurious, or at least not necessary for the 
healthy development of the plant, though in the earth they may 
assist subsequent nutrition by dissolving substances which could 
not otherwise pass into the plant. 4. To act as a reservoir of 
nutriment. 
The office which the root performs, of fixing plants in those 
situations where food can be obtained, is evident, and needs no 
further remarks. It is also essential to the proper performance 
of its absorptive powers. 
Absorption by the Root.—The function which the root per- 
forms of absorbing nutriment for the uses of the plant, from 
the materials in or upon which it grows, is not possessed by its 
whole surface, but is almost exclusively confined to the cells and 
root hairs (figs. 128 and 248) of the newly developed portions 
and young parts adjacent to them; and even these parts can 
only absorb when they are in the closest contact with the particles 
of soil by the root-hairs. Hence, in the process of transplanting, 
it is necessary to preserve the young growing roots as far as 
possible, otherwise the plants thus operated upon will languish 
or die, according to the amount of injury they have sustained. 
The injury done to plants in transplanting is also to a great extent 
influenced by atmospheric circumstances, and conditions of the 
soil at the time in which such an operation is performed ; thus, 
under the favourable circumstances of a warm soil and moist 
atmosphere, the destruction of a large portion of the young 
extremities of the root will do but little injury, as the plant 
will then speedily form new absorbent extremities; but if the 
conditions of the earth and soil be the reverse, then a large 
destruction of the young extremities of the roots will cause the 
plant to die before new absorbent extremities can be formed. 
Special attention should be paid to the above facts when 
transplanting is performed in the growing season ; but it is far 
better, when possible, to transplant late in the summer or in 
the autumn when the growing season is drawing to a close, or 
in the spring before it has recommenced, as at such periods 
little or no absorption takes place and the plants have accordingly 
time to recover themselves before they are required to perform 
any active functions. (See page 819.) 
This absorption of food by the youngest rootlets is due to 
osmose taking place between the contents of their cells and the 
fluids of the surrounding soil. But it should be noticed that, as 
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