PROCURING OBJECTS. 73 



strength of the branches of the tree. This section also ex- 

 hibits in coniferous trees (as the pine, &c.), the beautiful disc- 

 like glands which adhere to the woody fibres. These are 

 beautiful objects, and sometimes require a power of 200 or 300 

 diameters. The tangental vertical section is a slice across the 

 medullary rays; it exhibits the form and arrangement of the 

 cellular tissue within them. All the vertical sections show the 

 form, size, and connexion of the woody fibres ; spiral, reticu- 

 lated, and dotted vessels, &c. ; and are far more instructive than 

 the transverse sections. 



Charcoal. Thin sections of charred wood are very interest- 

 ing and instructive. 



Fossil Woods. Thin sections must be made by grinding on a 

 lapidary's wheel. They should be polished. 



Siliceous Cuticles, &c., from equisetum, straw, cane, &c., 

 are prepared by heat in a covered crucible, or by boiling and 

 digestion in nitric acid. The most favorable example for 

 showing the form in which silica occurs in plants, is the husk 

 of the oat or wheat. If a husk of oat be examined under the 

 microscope, having been mounted in water or Canada balsam, 

 a series of bright parallel columns, serrated on each side, may 

 be observed among the cellular tissue : if another specimen be 

 burned carefully between the glasses, and the ashes be mounted 

 in balsam, the siliceous columns will still be seen. In the 

 ashes of the husk of wheat, rows of concave discs may be 

 observed, which are composed of some metallic oxide. In the 

 ashes of the calyx and pollen of the mallow, organized lime 

 may be detected. In the ashes of coal, a variety of vegetable 

 structures, as cellular tissue, spiral vessels, &c., may be dis- 

 covered. In these experiments it is necessary to render the 

 ashes transparent by immersion in balsam. 



Hairs, Down, &c., from leaves and stems, are generally 

 opaque objects. In the plants which produce cotton, the hairs 



7 



