FUCUS SERRATUS 203 



contain only barren hairs, and they may be termed sterile or 

 neutral conceptacles. 



MICROSCOPIC EXAMINATION. 



II. As it is almost impossible to make satisfactory prepara- 

 tions of the tissues of Fucus from fresh material, it will be 

 found a great advantage to fix and harden them : the material 

 is to be fixed by treatment with a solution of picric acid in sea- 

 water, and after washing, to remove excess of picric acid, it is 

 hardened in successive strengths of alcohol. An alternative 

 method, which gives good results, is to treat the specimens first 

 with i per cent, chromic acid, wash with water, and harden in 

 successive strengths of methylated spirit. 



From material thus prepared select a young flattened branch 

 of the thallus in which the midrib is but slightly 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 : recognize 

 especially 



a. A compact marginal band of tissue of a yellowish-brown 



colour, the cortical band : this graduates off into 



b. 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 



i. 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, continu- 

 ously meristematic 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 cuticularized, the walls of 

 these cells are thin, and the protoplasm plentiful, with a 

 nucleus. 



