MICROSCOPIC OBJECTS. 89 



spiral or other vessels. It is clear from the above 

 observations, that with three of these thin sections — the 

 whole not weighing more than a grain — the growth and 

 characters of a tree can be determined. Mr. Pritchard, 

 who first introduced these thin sections as microscopic 

 objects, says that he always arranges them in the follow- 

 ing order : under the name — ^first, the transverse section ; 

 second a radial vertical section ; third, a tangental verti- 

 cal section. In the shdes containing endogenous plants, 

 there are only two. sections — that immediately below the 

 name — transverse; and the other vertical. 

 • Teak, {Tectona grandis). — ^The wood of this tree is 

 said to contain an abundance of silex, which may be 

 tested by submitting a thin section to polarized light. 

 To facilitate the operation of cutting thin sections of 

 woods, it is usual to immerse them in such fluids as will 

 dissolve out of them any hard substance ; and where 

 silica is present, caustic potash is employed to remove it. 

 A specimen so treated will not, of course, depolarise light. 



Yeast Globules. — It appears from Mr. Latour's micro- 

 scopic experiments on fermentation, that yeast consists of 

 a congeries of minute vegetables, which are propagated 

 with amazing rapidity at a moderate temperatm^e. See 

 Phil. Journ. vol. xxv. (1838) p. 357. 



Organic Fabrics. — ^There is a vast variety of articles of 

 this nature, which not only possess much interest, arising 

 from the methods by which the threads or bundles of 

 fibres are woven or interlaced, but are of much import- 

 ance in a useful, ornamental, and even commercial point 



