APPENDIX. 83 



require greater care in grinding, in consequence of being 

 more brittle. The polishing, however, may be dispensed 

 with, and the section mounted in balsam. 



STONES OF VAKIOUS KINDS OF FRUITS (Plate 8, Fig. 232) 

 will well repay the labour bestowed in producing good 

 sections. The saw, the file, and the hone are the principal 

 agents used in the reduction of these hard osseous-like 

 tissues. A perfect section should have but one layer of cells, 

 which may be admirably seen when mounted in a cell with 

 weak spirit. 



SECTIONS OF WOOD (Plate 3, Figs. 49 to 55). To make 

 thin sections of hard wood it will be necessary to employ some 

 kind of cutting-machine. There are several of these, more or 

 less expensive, but the principle of constructionin all is similar. 

 The wood, after some preparation, and being cut to the requisite 

 length, is driven by a mallet into a brass cylinder, at thebottom 

 of which works a fine screw with a milled head. The wood is 

 pushed to the surface of the tube, and to any degree above 

 it by the revolution of the screw ; when a sharp knife, ground 

 flat on one side, is brought with a sliding motion in contact 

 with it. The slices may be removed from the knife by a 

 wetted camel-hair pencil, placed in some weak spirit, and 

 examined at leisure ; the thinnest and most perfect section 

 being retained for mounting. Green wood previous to being 

 cut should be placed in alcohol and afterwards in water. 

 Hard and dry wood may be made sufficiently soft for slicing 

 by first immersing it in water for some days. Sections of 

 the above may be mounted either in balsam or fluids. Stems 

 of plants, horny tissues, and many other substances not 

 sufficiently hard to be ground down, may be cut into slices 

 of extreme thinness by this handy instrument. 



CUTICLE OF PLANTS (Plate 2, Figs. 37 to 41), HAIES 

 (Plate 3, Figs. 69 to 82), AND SPIRAL VESSELS (Plate 2, 

 Figs. 42 to 45), may all be obtained by macerating the 

 leaves and stems of plants in water, and afterwards dissect- 

 ing them with the needles. Good specimens of the cuticle, 

 showing the stomata, may be often obtained by simply 

 peeling off the skin with a sharp knife. Hairs may be de- 

 tached from various parts of a plant by a similar process. 

 Spiral vessels will, however, require to be separated by the 

 needles from the surrounding tissues. All delicate vegetable 

 preparations are best displayed when mounted in a cell with 

 weak spirit. 



Cells for mounting objects in fluid are generally formed 

 of some kind of varnish upon which the fluid will not act : 



