98 PROTOPLASMIC CONTINUITY IN THE FtJCACEiE. 



"water for a few minutes and then stained with methyl green, 

 acidulated with acetic acid. After well washing with water or 

 acetic acid, the sections were put for a short time — varying in 

 different cases — into alum-carmine. They were again well washed 

 with water, swollen with strong ammonia and mounted in 

 glycerine. Sections prepared in this way turn out in a very 

 pretty condition, the protoplasmic structures being coloured green, 

 and the framework a pale pink or violet. Before swelling with 

 ammonia the sections must be thoroughly washed, to remove all 

 traces of alum, as otherwise the ammonia will cause a precipitate 

 of alumiuic hydrate to be thrown down. 



B, For the determination of more refined details, the sections 

 were treated as follows: — Having been washed with fresh water, 

 they were stained with an aqueous solution of safl'ranine ; again 

 washed with water and swollen with strong ammonia ; and finally 

 mounted in glycerine. Thus prepared, the sections showed the 

 protoplasts of a pink colour and their envelopes yellow, deepening 

 here and there to brown. 



C. Still more satisfactory results were, however, obtained 

 thus : — Sections were soaked for from 3 to 12 or 20 hours in a 

 mixture of strong sulphuric acid, 1 part, and water, 3 parts. 

 They were then washed, stained with saffranine as in the preceding 

 process, and mounted in a mixture of glycerine and ammonia. If 

 the ammonia is employed to swell the sections before mounting, 

 they become so much disintegrated that it is then impossible 

 to transfer them to a slide. 



ASCOPHYLLUM NODOSUM Le Jolis. FuCUS NODOSUS L. 



The frond of this Fucoid is so common and abundant on British 

 coasts, and its appearance is so well known, that there is no need 

 to give any description of its general morphology. It is only neces- 

 sary to refer to the leading features of its histological structure. 



In longitudinal sections of any part of the thallus, made 

 perpendicular to the flattened surfaces and examined under the 

 microscope, we may distinguish, with more or less clearness, an 

 epidermis, a cortex, and a central or medullary tissue. PI. 255, 



The epidermis is composed of a single layer of small cylindrical 

 cells, averaging 0*0005 inch in breadth, and from 1^ times to twice 

 this in length. They are placed with the long diameter per- 

 pendicular to the thallus, and are somewhat strongly cuticularised on 

 the free surface. In the fresh state the lumen of the cells is filled 

 with a dense, granular, brown-coloured protoplasm, and the walls 

 appear of no great thickness. In the dried condition, the proto- 

 plasm is contracted, and the true thickness of the walls is obvious. 



The cortex consists of 3, 4, or more layers of cells, of a 

 somewhat more irregular shape than those of the epidermis, — the 

 cells of each layer forming a longitudinal series. The cells in 

 contact with the epidermis hardly measure more than 0"0005 inch 

 by 0-0005 inch, but, passing from without inwards, the cells 

 become larger and more elongated hi the longitudinal direction, 



