FUCUS. 53 



conceptacles (fasergrulcheri) ; these will then appear (if 

 cut through the ostiole) as an irregularity of the cortical 

 band. If the conceptacle was young, it would be found 

 to be a still closed cavity of considerable size, filled with 

 mucilage, and with hairs which originate from single 

 cells of the tissue lining the cavity ; in sections of older 

 parts the ostiole would be found widely open, the hairs 

 much longer, and protruding out of the conceptacle : 

 these hairs may be observed even with the naked eye 

 on the older parts of the thallus. 



III. Cut longitudinal sections of a young part of a 

 thallus (i.e. close to the apex of a branch), mount in 

 pure glycerine, and examine under a high power : 

 recognise, as in the transverse sections, the cortical 

 band, consisting of 



1. The limiting layer, which presents similar 

 characters to those seen in transverse sections. 



2. The inner parenchyma : note that the cells of 

 the inner part of this tissue are arranged in longitudinal 

 rows, having relatively thick, occasionally pitted, lateral 

 walls, and thin transverse septa: this tissue merges 

 gradually into 



3. The medulla, which consists of " trabecular " 

 tissue : here longitudinal rows of cells constitute fila- 

 ments resembling the hyphse of Fungi, with numerous 

 thin transverse septa, to which the protoplasmic contents 

 closely adhere : as already seen in transverse section, the 

 longitudinal walls consist of a firm, highly refractive 

 cellulose coat embedded in a mucilaginous matrix. 

 Note the frequent lateral communications of the fila- 

 ments, and compare them with the pits in the cortical 

 tissue, to which they undoubtedly correspond. 



