232 VEGETABLE PHYSIOLOGY 
wood, we find stores of food laid up in the region just under- 
neath the surface, which constitutes what is called the 
cortex, and which gives place later on to the complex forma- 
tion that is familiar to us under the name of bark. 
The formation of the successive rings of cork deeper and 
deeper in the cortex, which ultimately constitute the bark, 
MT. wpe 
Fia. 106.—Srorion or THREE-yEAR-oLp Stem or Tilia, SHOWING THE 
Meputiary Rays RUNNING THROUGH THE Woop. xX 560. (After Kny.) 
is attended by the same need of a continuous instead of an 
intermittent supply of food. We find, therefore, during 
the process of the construction of the bark, similar pro- 
vision of food-containing tissue, which is situated near the 
cork layers. In some cases it takes the form of regular 
sheaths ; in others the food is irregularly distributed through 
the cortex, which is the seat of the appearance of the forma- 
tive layers of the cork. 
