1882.] 



MICROSCOPICAL JOURNAL. 



223 



energetic oxidation of the endo- 

 chrome by the permanganate. In 

 fact, if the diatoms are then exam- 

 ined with the microscope, their entire 

 organic matter will be seen coagulat- 

 ed, brown or black and already 

 greatly modified. By the addition of 

 the acid, there ensues a disengage- 

 ment of oxygen, which burns up, and 

 of chlorine which decolorizes : it is 

 undoubtedly to these different and 

 successive reactions that the perfect 

 cleanliness of the silica, without cor- 

 rosion, is to be attributed. In fact, 

 the surface of the diatoms appears 

 pure, and with all its lustre : it has 

 lost its organic envelope, and the 

 finest details (striae, punctations) are 

 clearly to be seen. 



I have tried the different chemical 

 methods that have been successfully 

 announced during late years, but I 

 have not found one of them which 

 succeeds so regularly. 



The Mounting of Pollen Grains. 



There are few objects more beau- 

 tiful, when properly mounted, than 

 pollen grains, and the variety of their 

 form is almost endless. They may 

 be mounted either dry or in fluid, but 

 in the latter case the proper liquid 

 medium should be chosen. Water is 

 not considered a good mounting fluid 

 for grains of pollen, and balsam is 

 not suitable. Perhaps one of the 

 best mediums is castor oil, which 

 clears the grains beautifully, and 

 shows their markings very distinctly ; 

 but it is an easy matter to experiment 

 with each specimen, using different 

 fluids, before mounting permanently. 

 Whether they should be mounted 

 dry or in fluid .depends upon the 

 taste of the mounter more than upon 

 other considerations. 



Dry mounts can be made by pre- 

 paring cells as for opaque objects, 

 and scattering the grains over the 

 bottom. Wax cells are excellent for 

 the purpose. They may be made by 

 cutting out circular pieces from a 

 sheet of olive-green wax, such as is 



used in making wax-flowers, by 

 means of a gun-punch, pressing this 

 upon the centre of the slide and plac- 

 ing a brass curtain-ring upon it. The 

 application of a gentle heat below 

 will soften the wax so that the ring 

 will sink into it sufficiently to hold, 

 or it may be pressed down by means 

 of a slip of glass without throwing it 

 out of place. The wax should not 

 be melted, for in that case it loses its 

 smooth surface and spoils the appear- 

 ance of the bottom of the cell. 



When the wax cools, put the slide 

 on the turn-table and finish up the 

 outside of the cell with any thick ce- 

 ment or varnish. We prefer to finish 

 the cells in this way before using 

 them for mounting. 



When ready to mount, dust in the 

 pollen grains and run a thin layer of 

 shellac around the top of the cell. 

 This soon becomes tacky, and the. 

 cover can then be immediately ap- 

 plied. After a few hours the cell may 

 be finished with black or colored 

 cement. 



Cells may also be made for pollen- 

 grains out of cement or varnish, and 

 the bottoms can be coated with some 

 dead-black paint, or the glass may be 

 left clear so that transmitted light 

 may be used. 



For mounting in oil the cell is best 

 made of plain shellac. It should be 

 just deep enough to protect the 

 grains from pressure when the cover 

 is applied. Shellac is a good cement 

 to fasten the cover down, so also is 

 hard balsam dissolved in benzole. 



Pollen grains usually make fine ob- 

 jects by reflected light, and one of 

 the most beautiful objects to be seen 

 is a rnass of pollen grains from the 

 morning glory displayed on a dark 

 background. The transparent mounts 

 should be examined with a parabola, 

 spot-lens or Webster condenser, so 

 as to display the grains on a dark 

 field. Many of the plants that bloom 

 indoors during the winter have very 

 beautiful pollen grains, so this article 

 cannot be out of season even though 

 published so late in the year. 



