ANATOMY OF TISSUES. 137 
There is, however, in many plants an actual separation of certain 
parts outside the periderm formation. (Fig. 59.) As before ex- 
plained, all portions outside the periderm gradually die for lack 
of food. Not all, however, are removed from the plant, certain 
portions of bark remaining to perform the functions of epider- 
mis, and some botanists refer to the bark as a third form of 
epidermis. In order to understand how some portions are 
S—= 
FIG. 59. 
a cork layer separating bark scales. e and / large parenchymatic rind cells. 6 an outer 
zone of thick-walled, a one of thin-walled cork cells ; the latter tears easily. cisa 
layer with only the outer wall thickened. d phelloderm. 
separated and others are allowed to remain, it will be necessary 
to describe more fully the elements of the inner periderm which 
differ slightly from those already described. These elements 
may be tabulated as follows: 
ae ‘ Cork. 
ellem 
Deep-seated eto: 
» Phellogen Initial or meristem layer. 
Periderm. 
| Pheloscnn ; Inside Pi, never corky 
nor lignified. 
The term phellem here is used for all the tissue cut off to- 
ward the circumference; that part of it whose walls become 
lignified is called phelloid, while all the cells cut off centrip- 
