GROUPS OF TISSUES, OB 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 



Fia. 33. — TransTerse section of one-year-old stem of Ailanthus. e, epidermis; 

 fc, corlc-cells; r, inner green cells; between fc and r a layer of cells filled with 

 protoplasm, called the phellogen, or cork-cambium. Magnified 360 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 



