GROUPS OF TISSUES, OR TISSUE-SYSTEMS. 53 
101. It is thus seen that in general the tissues of the 
fundamental system are so disposed that the periphery is 
harder and firmer than the usually soft interior, although 
there are many exceptions. This general structure has 
given rise to the term Hypoderma for those portions of the 
fundamental system which lie immediately beneath or near 
to the epidermis. Hypoderma is not a distinctly limited 
Fiq. 33.—Transverse section of one-year-old stem of Ailanthus. e, epidermis; 
k, cork-cells; r, inner green cells; between k and r a layer of cells filled with 
protoplasm, called the phellogen, or cork-cambium. Magnified 350 times. 
portion—in fact, it is often difficult to say how far it does 
extend; however, it usually includes several, or even many, 
layers of cells, or the whole of each of the tissue-masses 
(e.g., thick-angled, stony, and fibrous tissues, etc.) which 
immediately underlie the epidermis. 
102. Cork.—Within the zone which the hypoderma in- 
cludes there frequently takes place a peculiar development 
of the young parenchyma, giving rise to layers of dead 
