The Plant 
39 
in by the root hairs from the soil, and also by the stomata 
of the leaves from the atmosphere, and there, in the 
chlorophyll-filled cells of the leaves, they unite, under the 
action of sunlight, to form very important plant substances, 
and this at the ordinary temperature of the atmosphere; 
while such changes, when carried out in a laboratory, require 
Organs for Removal of Substances 
an enormous amount of heat. When we examine the 
tissue of the leaf we find how Nature has arranged the 
cells to get the greatest amount of work done for the space 
taken up, and also how the cells have been arranged to 
prevent any damage from excessive heat of the sun. 
Wherever the heat of the sun comes into direct contact 
with chlorophyll it kills it, but the cells on the upper side 
of the leaf are elongated, running from the epidermis into 
the centre of the leaf, and the chlorophyll corpuscles are 
