THE ROOT 23 
altogether. The spring cells are larger than the rest for 
two reasons—first, there is more sap running in the tree, 
and the cells fill out better; and second, the jacket of 
DIAGRAM OF ROOT. 
bark has been split with the winter cold, and stretches 
more easily. Towards the autumn it has grown hard and 
dry and fits more tightly. Under the pressure all round 
the new wood-cells are more tightly packed. Then comes 
the winter’s rest and next spring more large-celled wood, 
the edge of which shows up distinctly against the autumn 
ring. - 
In the root the bundles very early form one central 
mass, the woody and bast sections inside, the cambium 
ring jacketing them closely, and giving rise to all the 
various side roots that spring out and help the plant 
by extending the area from which it gets its food-supply. 
