382 PEACTICAL BOTANY 



it may then be seen in those sections which pass 

 through the middle of one of the tiers of cells above 

 noted that 



1. The section is circular, since the thallus is 

 cylindrical. 



2. That it is limited externally by a clearly marked 

 cuticle, and it will be remembered that as Asco- 

 phyllum, on which it grows, is found about half-tide 

 mark, the plant is exposed to the air for several hours 

 in each tide. 



3. The series of pericentral cells, of variable 

 number, each surrounded by a massive, stratified cell- 

 wall, and having a dense, highly refractive, protoplasmic 

 body. 



4. The single large central cell, having similar 

 characters of wall and protoplasm to the pericentral 

 cells. 



5. Note especially the protoplasmic strands, which 

 run from the central cell to the several pericentral cells, 

 traversing the cell-wall. 



The recognition of these connecting strands of protoplasm 

 between the cells of the thallus of the Florideae dates back to a 

 period before "protoplasmic continuity" had acquired the special 

 interest which it now possesses ; nevertheless, there is still some 

 difference of opinion as to the details of their structure : some 

 hold that, at least in some cases, the strands are continuous, with- 

 out any break, from one cell to another ; that this is not the case 

 universally is obvious, as pit-membranes may be seen (and 

 clearly in the majority of cases in P. fastlgiata) traversing the 

 strands transversely. It has further been ^asserted that, where 

 this is the case, the pit- membrane has the character of a sieve ; 

 but still Schmitz holds that there is no exchange of protoplasm 

 as such, since the pit-membrane is covered on either side by 



