76 



QUEKETT'S LECTURES ON HISTOLOGY. 



plant, in its time, becomes hard, and to no definite combina- 

 tion of cells can we apply the term skeleton. Nevertheless, 

 the deposition of inorganic matters in the interior of the cells 

 of plants, in a manner resembling the process of ossification in 

 the animal kingdom, is a fact of great interest. Here, as in so 

 many other instances of vegetable structure, we see the com- 

 mencement of the processes which have great significance 

 when carried on in the animal kingdom. The following 

 oljservations on the siliceous deposits in the cells of plants 

 will illustrate this remark. 



" In plants, as I have before stated,* inorganic salts occur in a crystal- 

 line form, under the name of ra]^hides ; these, however abundant, may be 

 regarded as accidental deposits, since it has been shown that they can be 

 produced by artificial means. For the benefit of those who may not have 

 l3een present on former occasions, I will give a few examples of the dermal 

 siliceous skeleton of plants. 



" The first specimen is a portion of the Equisetum hyemale, fig. 2, which 

 has been boiled for a long time in nitric acid, and not only exhibits the 

 cells of the cuticle, with their serrated edges, but also longitudinal rows of 

 oval bodies, which ai"e the stomata. Another good example is a portion of 

 tlie husk of the Wheat, fig. 3, in which, in addition to the cells of the 



Fia;. 2. 





, .MA 



Fig. 3. 



A portion of the cuticle of £qui- 

 setum hyemale, after long boiling 

 in nitric acid. 



A portion of the husk of a grain 

 of ^yheat. 



cuticle, the spiral vessels, recognized by the coiled-up fibre, also liave a 

 skeleton of silica. In the husk of the Rice the peculiar cells of the cuticle 

 are seen, with bundles of woody fibre and vessels below them. The 

 specimen is composed entirely of silica, and there may be noticed in one 

 spot, where the cuticle has been torn, a series of elongated fusiform bodies, 

 with serrated edges, fig. 4, which are all that remain of the woody fibres' 

 proving that in this plant the silica is not confined to the cuticle. All 

 the fibres, however, are not thus serrated ; some, as represented at h, may 

 be seen in bundles, which are both longer and thinner than tlie first 

 mentioned, with perfectly smooth edges. 



" On the upper surface of the leaf^of a plant common in our gardens— 

 the Dcutzia s'jaSra— there are numerous stellate hairs, which much 

 resemble Star-fishes in miniature, fig. 5; these are covered with little 



* Histological Lectures, Vol. I., p. 42. 



