510 



MR. S. LE M. MOOEE S STUDIES 



5. 



3. Of their behaviour resembling in almost every point 

 that of the cell-protoplasm, and differing in almost 

 every point from that of the wall ; 



4. Of the evidence of differentiation as shown by boiling 



with Millon's fluid — this not being shared by the wall ; 



Of the behaviour of the stoppers with Schulze's macera- 

 ting fluid, viz. dissolution into adjacent plasma-balls, 

 which subsequently stain brown with iodine while the 

 wall remains colourless ; 



it seems impossible to avoid the conclusion that, although they 



resist gastric digestion, the stoppers consist of proteid. It also 



seems impossible to believe them to be formed by swelling-up of 



the wall, for why should such marked proteid reactions, and such 



different behaviour generally, be shown by the swollen portions 



alone ? We have also seen the pit cleared of its plasma and its 



mouths freed from stoppers ; and the appearance of the wall, in 



this case, is such as to put an emphatic veto on the swelling-up 



idea. Study of development of the stoppers, so far as it is 



practicable from dried specimens, teaches the same lesson. Let 



us look at a young cell — the youngest in which the stoppers are 



visible : we see here a tiny sphere of substance, looking exactly 



like the protoplasm and quite unlike the wall, placed at either 



end of a fine and apparently continuous pit, of which the 



lumen is occupied by a thread of protoplasm. These spheres 



we can see increasing gradually in size as we pass away from the 



growing region, and in no case can the least participation of the 



wall in this increase be detected. At length after cortication 



has set iu, the stoppers become of relatively enormous size, and 



frequently have bands of slimy substance attached to them ; this 



substance reminds one of the " Schlauchkopf " of sieve-tubes, but 



it may perhaps be true protoplasm. The point to notice here is, 



that not even in these old cells, the stoppers of which give 



precisely the same reactions as the younger ones, can any 



swelling-up of the intercellular wall be detected. I see no way 



therefore of escaping the conclusion that, like the callus of the 







Marrow 



at the pit's mouth of proteid matter derived from the proto- 

 plasm. 



Should the substance of the stoppers— which, like Vegetable- 

 Marrow callus, is insoluble in neutral saline solutions— be included 

















. ..'J 



