1918] SINNOTT—FOOD RESERVE 167 
species starch is poorly developed here even in summer. It is in 
these regions, too, that the “‘transitional’’ material is very apt to 
appear. Furthermore, even in typical starch trees the wood paren- 
chyma cells or ray cells which directly adjoin a vessel frequently 
contain fat; and in species where both starch and fat occur in the 
wood the fat is conspicuously abundant near the vessels. In the 
medullary rays of such forms as most of the poplars and willows, 
for example, fat is found chiefly in those ray cells which touch a 
vessel and starch in those which adjoin nothing but fibers. This 
tendency for starch to be absent and fat to be present in the imme- 
diate vicinity of the vessels is obvious in all woody plants in the 
midwinter season, and suggests that the character of the food 
reserve may be related in some way to the water supply. 
Another anatomical feature which is clearly associated with the 
kind of food stored in a cell is the character of the cell wall. Wher- 
ever this is strongly lignified, thick, and provided with few and 
small pits, starch tends to remain unchanged throughout the winter. 
When it is thin or provided with many and large pits, starch tends 
to disappear and fat to be abundant. Thus in the storage cells 
of phloem and cortex, the walls of which are quite unlignified, 
starch vanishes early and completely and fat is very common. In 
the heavily lignified, thick-walled pith cells which occur in so many 
species starch remains throughout the winter, and in such cells the 
reserve food is less modified than in almost any other part of the 
stem. In branch gaps, where such a pith meets the cortex, the line 
between the starch-containing and the fat-containing cells is abso- 
lutely sharp and coincides exactly with the line between the lignified 
and the unlignified tissue. 
A study of the vertical and ray parenchyma of the wood, the 
chief seats of food storage in the xylem itself, is particularly instruc- 
tive in this connection, and furnishes us with a definite anatomical 
distinction between starch trees and fat trees. Where these cells 
are thick-walled and have few and small pits, starch predominates; 
where the walls are thin and well pitted, fat predominates. In 
hard-wooded species (fig. 1), long noted as starch trees, the paren- 
chyma shares certain of the characters of the other wood cells and 
has thick, well lignified, square-cornered, and small-pitted walls. 
