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, 



m.r: 



FIG. 106. SECTION OF THREE-YEAR-OLD STEM OF Tilia, SHOWING THE 

 MEDULLARY RAYS RUNNING THROUGH THE WOOD, x 60. (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. 



