Green Leaves at Work 89 
shaken themselves after their long winter sleep, 
they set to work, for, fair though they are, beauty 
is not their sole excuse for being, and there is 
plenty for them all to do in Nature’s great gar- 
den. 
Through every leaf there runs a network of 
delicate woody threads, curving, branching, and in- 
terlacing. 
Its ramifications continue beyond the limits of 
unaided vision. We call it the ‘‘skeleton,” and 
it does fulfil an office similar to that of the bones 
in the human frame, for it supports the leaf and 
gives it shape and strength. 
But it also serves the leaf as veins and arteries 
serve the body, for the life-giving sap creeps 
through these woody threads in slow but continu- 
ous circulation. 
With the aid of a powerful microscope we can 
see that the green pulp of the leaf looks some- 
what like a honeycomb, as it consists of number- 
less cells laid row above row. Those on the 
upper side of the leaf are generally long and 
narrow, and stand upright, pressing together al- 
most as closely as the bricks in the side of a 
house (Fig. 16). 
But the lower leaf cells differ greatly one from 
