﻿264 



Evans: The genus Plag] 



strated in the epidermis and are often large and conspicuous, but 

 in certain species their size is very variable and depends on external 

 conditions. 



The epidermal pores of the thallus as noted by Leitgeb, are 

 of two distinct types. In the first (FiG. i) the opening is small 

 and often difficult to demonstrate, especially when more or less 

 stopped up by the waxy secretion on the cuticle. Around this small 

 opening there are usually from four to six bounding cells, the radial 

 walls between which are normally more or less thickened. Some- 

 times one or more of the bounding cells will be divided by a 



