40 VEGETABLE PHYSIOLOGY. [LESSON 13. 



provided with coarse serratures on their internal margins, their ends 

 are attenuated (reduced, made thin) and accuminated (pointed). 



235. The Dutch rush used to be employed extensively by cabi- 

 netmakers, to smooth their work, preparatory to polishing it, but 

 since the introduction of glass or sand paper, of various degrees of 

 fineness, it has fallen into disuse with these artisans ; it is still great- 

 ly employed, however, by plaster-of-paris figure makers, to file down 

 the seams left by the junction of the several parts of their piece- 

 moulds, and for this purpose it is invaluable. 



236. The Bull-rushes, and all the plants of this order, also con- 

 tain large quantities of silica. 



237. Silica, however, is not by any means restricted to the 

 Grasses; it enters into the composition of a vast number of plants, 

 in some of them associated with the cells of the bark in others with 

 the cells of the cuticles of the leaves. 



238. In the latter situation it is found in a very common garden 

 shrub, which has no vulgar name, the Deutzia scabra ; on the upper 

 cuticle may be seen a series of large, exquisitely beautiful stellate 

 crystals of flint, of (comparatively) large size(Fig 71). 



Fm. 71. 



Upper cuticle, Deutzia scabra. 



239. On the upper cuticle, the stars are composed of from 3 to 

 f) radii, four and five rays, however, being the most abundant. 



240. The under cuticle has a much more dense number of smaller 

 stars, placed nearer together, and the rays of which amount to from 

 10 to 13 (Fig. 72). 



