BOTANICAL MICROTECHNIQUE. 



433- To produce it, one may use a 10$ solution of salt- 

 peter to which a little eosin has 

 / been added. This pigment has 



the double advantage of at once 

 staining the killed part of the pro- 

 toplasm and of causing a sharper 

 definition of the uncolored cell- 

 sap. Pretty large Spirogyra**\\*. 

 furnish excellent objects for study 



remains of the dead chloroplasts. / t - s- \ 



(CI. Tig. DO). 



434. For fixing the isolated vacuolar membranes Went 

 recommends (I, 314) J-i$ chromic acid, which he allows 

 to act one or two days. He then washes the objects in 

 running water six hours and transfers them, in the usual 

 way, to paraffine, for the preparation of microtome sections, 



18. Methods of determining whether certain Bodies lie In the Cyto- 

 plasm or in the Cell-sap. 



435. This question often cannot be answered by direct 

 microscopical examination, and already various methods 

 have been devised which make a certain decision possible 

 even in difficult cases. Wakker (I) observed, with micro- 

 scope tipped down, what motions the bodies in question un- 

 derwent with the slide in a vertical position. If they simply 

 fall downward in the cells in a vertical line in consequence 

 of their greater specific gravity, it is very probable that the 

 bodies lie in the cell-sap. But, since the starch-bearing chro- 

 matophores of the starch-sheath, which undoubtedly lie in 

 the cytoplasm, sink down rather rapidly in the cells, as was 

 recognized by Dehnecke (I, 9) and Heine (I, 190), it has 

 seemed useful to me to modify this method by reducing the 

 ready displaceableness of the protoplasm by killing the 

 cells, which may be easily done with an iodine and potas- 

 sium-iodide solution. The movement of the chromato- 

 phores in the starch-sheath was at once stopped by iodine 

 solution, while the protein crystalloids in the epidermis of the 

 leaf of Polypodium irreoides, which undoubtedly lie in the 



