THE ROOT 61 
may best be seen by scraping the paper off the jar on 
the side opposite the slit. 
The turning away of the root from the light is 
exactly what one would expect, since water is generally 
to be found in the soil where no light exists. Light 
would, as it were, act as warning to the root that it 
was in the neighbourhood of a region where water 
would not be plentiful. The root is not, of course, 
conscious of the warning but is so constituted that it 
responds as though it were. These tropisms of roots 
are due to the irritability of the protoplasm, 7.e., the 
power of the protoplasm to respond to external 
influences. 
Root Cap.—The root, we have seen, bores its way 
into the ground. In its course, it must, of necessity, 
push against the soil grains, and may, quite frequently, 
eome into contact with hard stones and rock. Now, 
wherever growth is actually taking place, the tissue or 
substance of the plant is very soft and delicate, as may 
be seen by splitting the tip of a young twig, or cutting 
through the extremity of a root-branch of any common 
plant. This soft, actively dividing tissue where new 
erowth is going on is the meristem. In the case of 
the stem, the meristem of the growing point is pro- 
tected by the arching leaves of the bud in which it 
terminates, and, since the stem does not have to push 
_ its way through solid soil, this is quite sufficient. The 
root has no such leafy armour, but is provided instead 
with a root-cap, which serves it better. The growing 
point, where lies the soft actively dividing tissue that 
forms new cells, is not at the extreme tip, but a little 
way behind it, and is protected by similar cells, which, 
cut off from the front of the meristem, have beecme 
firmer and been pushed outward to form a kind of 
barrier against the rough soil grains. This barrier is 
the root-cap, the outer surface of which is being 
constantly worn away by friction with the soil, and 
