1918] SINNOTT—FOOD RESERVE * 169 
cells precisely like those of starch trees. This type of ray cell is 
here evidently mechanical in its function, since all these species 
have wide rays which might collapse or be badly crushed were they 
not built of strong-walled cells. The vertical parenchyma of these 
soft-wooded starch trees tends to have thinner walls, and in Lirio- 
dendron, at least, it contains considerable fat. 
On the basis of these facts we are forced to conclude that the 
hardness of a wood affects the type of food reserve indirectly, 
ees ees | S| ae Tl 
Fic. 2.—Populus grandidentata, a fat tree: medullary ray of wood seen in radial 
section“as it crosses fibers (at left and right) and a vessel (in center); note thin-walled 
ray cells, with slanting or rounded ends, and large pits from ray cell to ray cell and 
from vessel to (marginal) ray cells. 
through its influence on the walls of the storage cells. In certain 
cases, however, this effect is evidently more direct. The hard- 
wooded species of Cornus, such as C. florida, are starch trees, and 
the soft-wooded ones, such as C. stolonifera, are fat trees, although 
there is no very striking anatomical difference between the paren- 
chyma cells of the two groups. The same fact is noticeable in the 
hard- and soft-wooded species of Viburnum and birches. In these 
Cases it is fair to assume that the high or low degree of lignification 
