FUCUS. 51 



marked : cut transverse sections from it, mount in pure 

 glycerine, and observe under a low power 



1. The elongated elliptical outline of the section. 



2. The more or less enlarged midrib. 



3. The grouping of the tissues exposed : recognise 

 especially 



a. A compact marginal band of tissue of a 

 yellowish-brown colour, the cortical band : 

 this graduates off into 

 I. The less compact central mass of the 

 medulla, consisting of a web of interlacing 

 filaments. 



Put on a high power, and examine the tissues in 

 detail. Starting from the periphery, observe that the 

 cortical band consists of 



1. A superficial or limiting layer of cells, regularly 

 arranged, and elongated radially ; the cells are not of 

 uniform depth, and examination will show that they 

 divide by periclinal, as well as by anticlinal walls ; in 

 fact they constitute an active, continuously rneristematic 

 layer, and accordingly the term " epidermis " cannot be 

 applied to it in the strict sense. With the exception 

 of the outer wall, which is thick and cuticularised, the 

 walls of these cells are thin, and the protoplasm 

 plentiful, with a nucleus. 



Treat a section with strong sulphuric acid : all the cell- walls 

 swell, and lose their definite outline, with the exception of the 

 outer layer of the superficial wall, which remains sharply 

 marked. Treat a fine section with Schulze's solution : the 

 cuticle will stain yellow, while the walls of the internal tissues 

 stain a pale blue. 



2. Immediately below the limiting layer, and separated 



E 2 



