12 
natural selection, it is of course a matter of indifference whether they 
are above or below the parent roots; and no factor of the environment 
has the least influence in determining the place of their origin or the 
direction of their growth. They spring out at right angles, in all direc- 
tions, and are straight. In water and in air they behave in exactly the 
same way. Exceptional length and negative geotropism would be appro- 
priate reactions on the part of the pneumathodes emerging under water, 
but since the roots will not grow into water nor into soil without free air, 
their formation in this situation must be too abnormal and too rare a 
mischance for natural selection to have evolved any adaptation to it. 
Absorption.—The same forces operate to draw water into the roots of 
plants which afterwards cause its movement to the leaves. There are— 
(1) Suction exerted by the tissues surrounding the xylem ends in the 
leaves, and ultimately due to evaporation from the leaves under the 
influence of the sun’s radiated energy. 
(2) The osmotic activity of the cells in the roots through which the 
water passes. The former is the major factor, and its dominance is 
more extreme in the coconut than in most plants. This is clearly shown 
by two facts, the first one being that dead tips of roots for some time 
continue to absorb water without any measurable decrease in the rate as 
compared with that which was present while they were alive, and the 
second one is that if the tips of active, growing roots are cut off and 
immersed in water with not more than 5 millimeters of the cut end emerg- 
ing into a saturated atmosphere, drops of water are not exuded from the 
cut surface; it merely remains damp. When roots are cut or broken in 
the ground, a gummy substance with a characteristic odor sometimes 
exudes, but there is neither bleeding of water nor of a dilute solution. 
However, water entering the roots through the living epidermis and 
passing through living cells of the cortex to the stele must move under 
the immediate influence of the osmotic activity of these cells; a move- 
ment of the water under natural conditions is thus effected because it is 
constantly withdrawn from the inmost layers by suction. In this way 
the turgor of the roots is a factor in the acquisition of water, even in 
those which never bleed. The absence of bleeding only demonstrates 
that the living cells of the root will not pass a part of their osmotically 
active substance along with the water to the xylem; high turgor in the 
roots and abundant water in the soil will not necessarily result in root 
pressure. 
The turgor in the pith, and in all except the fine outer cells of the cortex of 
the absorbing zone of the roots, equals 0.25 to 0.3 normal potassium nitrate 
solution. The walls are so thin that they wrinkle everywhere when plasmolysis 
is extreme (fig. 5). In the fine cells, which later become the hypodermis, plas- 
molysis is not visible in a less concentration than 0.5 normal; it is possible that 
the denseness of the protoplasm, together with the osmotic pressure caused by 
the cell sap, is responsible for this rather high figure. Plasmolysis is hard to detect 
in the epidermis. The turgor usually, but not always, seems to be a shade higher 
