106 Mr W. Gardiner, On the constitution of the cell-wall. [Feb. 11, 



ture, and also, on account of the rapid constriction of the pits, tends 

 to be held firmly in position. When by plasmolysis, &c, one 

 attempts to contract the pit processes to the main protoplasmic cell- 

 mass, the particular portion next the pit-closing-membrane usually 

 remains behind, and on account of its subsequent rounding off, 

 presents the appearance of a lenticular body as induced for instance 

 by the action of calcium chloride. But in other cases when, owing 

 to the particular combination of forces, the whole of the pit-proto- 

 plasm endeavours to separate, then the delicate closing membrane 

 becomes clearly apparent. 



The portion of the pit-protoplasm next the pit-closing-mem- 

 brane is usually well differentiated, and on that account, and on 

 account of its peculiar form, has been distinguished both by 

 Schmitz 1 and also by Perceval Wright 2 , the latter of whom 

 appropriates to it the name "stopper", and states that in every cell, 

 at least two of these stoppers are present. 



Thus so far as I have been able to observe, a pit-closing-mem- 

 brane is always present, both in the cortical, and the central cells, 

 which may be extremely difficult to bring into view, as in the 

 Polysiphonias, but in certain other cases may be seen with com- 

 parative ease. There is little doubt that the closing membrane 

 consists of cellulose, and that it is perforated in a sieve-like manner 

 as Schmitz has already described for many of the Florideae. I 

 also believe from my somewhat scant experiments with preserved 

 material, that in the Corallines the same structure occurs as in the 

 rest of the Florideae. 



Passing to other matters I find that Wille 3 has observed a con- 

 tinuity of the protoplasm in Stigonema compactum, and I also, 

 before I was acquainted with Wille's researches, found the same 

 to occur in the case of Nostoc. In Volvox globator, so far as I 

 have been able to investigate it, I believe that a similar continuity 

 exists. 



1 Schmitz, loc. cit. 



2 Perceval Wright, loc. cit. The name was first employed by Archer. See his 

 paper " On the minute structure and mode of growth of Ballia callitricha," Trans. 

 Linn. Soc. ser. 2, i. p. 211. 



3 Wille, Ber. Deutsch. Bot. Gesell. i. 1883. Wille also finds a nucleus in the 

 cells of Tolypothrix lanata, thus confirming Schmitz's discovery of the presence 

 of a nucleus in the Phycochromaceae. If Guignard's statement with regard to the 

 nucleus of the sieve-tubes of Vitis be confirmed (Bull. Soc. Bot. France, xxviii. 

 pp. 332 — 333, 1881) it can hardly be doubted that a nucleus is present in every 

 living cell whatsoever. 



