1884.] of the cell-wall and middle-lamella. 105 



This being the case, it will be noticed that the author has 

 simply repeated anew, the observations made in 1878 by Perceval 

 Wright 1 and Thuret 2 , and is apparently unacquainted with the 

 researches of Schmitz 3 , who has showed that except perhaps in the 

 Corallines a pit-closing-membrane is present in each cell, which is 

 usually perforated in a sieve-like manner. I have myself investi- 

 gated several of the Florideae, and I find, that in all the cases 

 which have come under my observation a distinct pit-closing- 

 membrane can always be made out after proper treatment. 



Of the existence of a continuity of the protoplasm between 

 neighbouring cells there seems but little doubt, and indeed, so 

 tenaciously do the jDrotoplasmic processes of the pits adhere to the 

 closing membranes that it is a matter of difficulty to demonstrate 

 that such a membrane exists; the protoplasm refusing to separate 

 even after the action of very strong plasmolysing agents. Thus in 

 the Polysiphonias which may be taken as typical representatives, 

 e.g. P. nigrescens, a treatment with strong sulphuric acid (as 

 observed by Thuret 4 ) or with strong salt solution, does not separate 

 the protoplasmic processes of the pits from one another, but on the 

 contrary every appearance of what one might conveniently speak 

 of as a direct, unbroken continuity exists. When on the other 

 hand, the fresh tissue is treated for some time with solutions of 

 calcium chloride or chlor. zinc, iod., previous to preservation in 

 alcohol a different appearance is produced. In the first case the 

 protoplasmic processes of the pits contract to the main protoplas- 

 mic mass of the cell, and in so doing leave a distinct pit-closing- 

 membrane which is swollen on both sides, giving to the whole 

 structure a lenticular form and recalling the torus which occurs 

 on the pit-closing membranes of certain bordered pits. After 

 treatment with chlor. zinc. iod. this lenticular doubly convex body 

 may also be left as a pit-closing-membrane, but in certain cases one 

 can detect that the membrane in question is further resolved into a 

 thin pit-closing-membrane, having on either side of it a small mass 

 which now possesses a plano-convex form. 



To explain these phenomena I have adopted the following 

 view, which however I do not consider as final, since I have not 

 investigated the subject as thoroughly as I could wish. The pits 

 of the Florideae and consequently the protoplasmic processes which 

 enter them rapidly narrow, from the pit-closing-membrane towards 

 the cell-lumen, so as to present a trumpet-like shape. Of the 

 processes themselves; that portion which abuts immediately on the 

 closing membrane, both adheres with great tenacity to that struc- 



1 See Perceval Wright's two papers, Trans, Roy. Irish. Acad. xxvi. 1879. 



2 Thuret, Etudes Phycologiques, p. 100, 1878. 



3 Schmitz, Sitzber. Akad. Wiss. Berlin, pp. 215—58, Feb. 22nd, 1883. 



4 Thuret, loc. cit. 



