ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 641 



will thus be clearly marked out. If, however, another section is 

 treated for a longer time with acid, or the same section is a second 

 time exposed to its action, no special coloration of the bottoms and 

 sides of the pits takes place on staining, but the whole swollen wall is 

 of a uniform light tint. This shows that the substance of the pit- 

 closing membrane and of the layers immediately surrounding the pit- 

 cavity are more resistent than the rest of the cell-wall ; as indeed has 

 already been pointed out by Strasburger. 



Exactly the same phenomena are observed when a section, after 

 cautious treatment with sulphuric acid, is stained with methyl-violet. 

 In the case of methylene blue the protoplasm is not coloured, but 

 when methyl-violet is used, a deep staining of that structure occurs, 

 the tint of which is the same as that of the bottoms and sides of the 

 pits ; for, w^hile the general cell-wall assumes a violet colour, the pro- 

 toplasm, the pit-membranes and the sides of the pits appear of a deep 

 purple. Now since protoplasmic processes from the main protoplasmic 

 mass may project for some distance into the swollen pits, when such a 

 stained section of pitted tissue is examined, it appears as if there were, 

 in any two contiguous cells, threads of protoplasm of a purple colour 

 traversing the thickness of the violet cell- wall by means of the pits, 

 and thus establishing a direct continuity of the protoplasm from cell 

 to cell. But after prolonged treatment with dilute glycerin, this 

 purple colour dissolves from the pits, and the protoplasmic processes 

 are left clearly seen, and may or may not be the means of establishing 

 a continuity between the cells. As in the case of methylene blue, so 

 also here, a more lengthy treatment of the tissue with acid will swell 

 up the pit-membranes, and when in that condition the pits will assume 

 the same colour as the rest of the cell-wall. 



Method of Preparing Dry Microscopic Plants for the Micro- 

 scope.* — G. Lagerheim has found the following method convenient 

 for the examination of algje or other plants which have already been 

 dried. 



A fluid is prepared of the following composition : — 1 part fused 

 potassium hydrate is dissolved in 5 parts water, and when the solu- 

 tion is complete 5 • 5 parts are added of glycerin of the consistency of a 

 syrup. The dried desmids, CEdogoniacese or other alg89, are treated 

 with water till they are thoroughly moist ; a small jiiece of the 

 material is then taken up with a pincette and placed upon the glass 

 slide. One or two di-ops of the fluid are added, and the algae 

 distributed as evenly as possible with dissccting-needles. The glass 

 slide is then warmed for a time over a spirit-lamp, and a cover-glass 

 finally placed on. The potassium hydrate has now caused the 

 previously shrunken alga) to swell and resume their original form. 

 The addition of glycerin gives a consistency to the fluid, so that the 

 algae can easily be turned over by shifting the cover-glass, and thus 

 observed «m different sides, a point of great importance, for example, 

 iu the study of desmids. 



♦ Hot. Cfiitralbl., xviii. (1884) pp. 183-4. 



