240 VEGETABLE PHYSIOLOGY 



just underneath the surface, which constitutes what is 

 called the cortex, and which gives place later on to the 

 complex formation 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 I the 

 bark, is attended by the same need of a continuous instead 



IX 



FIG. 110. SECTION OF THREE-YEAR-OLD STEM OF Tilia, SHOWING THE 



MEDULLARY RAYS RUNNING THROUGH THE WOOD. X 50. (After Kny.) 



of an intermittent supply of food. We find, therefore, 

 during the process of the construction of the bark, similar 

 provision 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 for- 

 mative layers of the cork. 



