602 MR. S. LE M. MOOBE S STUDIES 



a steadying force whereby the shock of plasmolysis is lessened, 

 especially at the opposite side of the wall, which is usually where 

 the threads occur. The demonstration of the threads is a matter 

 of cautious treatment with water, for, if the iodine tincture be 

 made too dilute, the cell-wall swells up violently, and the threads 

 are broken ; however, it often happens that they can still be 

 distinguished in the form of frays upon the edge of the contracted 

 pellet of protoplasm (fig. 4) . S. potatorum differs from its con- 

 geners in the minute pitting of the cell-wall : the pits in ordinary 

 section are seen to be very narrow slits ; in oblique section they 

 present a pectinate appearance upon the wall (figs. 18 & 19). 



I have also, on very rare occasions, seen plasmolytic threads in 

 sections of the endosperm of Diospyros embryopteris treated for 

 several hours with chloriodide of zinc, and stained with picric 

 blue. Years ago Pringsheim * showed that such threads could be 

 seen in cells of fern-prothallia, Riccia, &c. acted upon by weak 

 chloriodide of zinc, but I was unprepared to find them after pro- 

 longed action of the strong reagent. Figure 13 represents the 

 best example obtained ; two only of the threads could be traced 

 with distinctness into intramural threads, the connection of the 

 rest not being patent. The threads, whether of Strychnos or of 

 Disopyros, stained well, those of the former with iodine, those of 

 the latter with picric blue. 



Continuity in the Floridecd. 



It lias long been known that the cells of certain Florideae are 

 placed in communication with each other by means of plasma- 

 containing apertures in their walls. A cursory examination of 

 Nageli's works t is sufficient to show that he had very clear con- 

 ceptions upon the subject. In the case of several genera (e. g. 

 Callithamnion, Laurencia, Peyssonellia) he figures pores which he 

 describes as having each a small elliptical opening in the centre ; 

 and it is plain from the context that he understood them to 

 function as organs of intercellular communication. Kiitzing t, 

 too, occasionally figures continuity ; and Zanardini §, in the text 



* ' Bau und Bildung der Pflanzenzelle.' 



t 'Die neuern Algensysteme ; ' On the Nuclei, Formation and Growth of 

 Vegetable Cells, Kay Society's volume for 1845 ; Sitzb. d. Konigl. Bayer. Acad. 

 1861. 



| ' Phycologia Generalis.' See tabb. 63, 65, 79, and others. 



§ ' Iconographia Phycologica Adriatica,' Chondrus ? adriaticus (tab. 38), and 

 Schizymenia minor (tab. 62). 



