THE VEGETABLE SECRETION OF SILICA. 



i?. 98. Silicious cuticle from the husk 

 of the wheat (Triticum), showing cups 

 for the insertion of hairs, and also 

 spiral vessels. 



The parts of plants in which the silica is chiefly found, are the external layers 

 of the cuticle, as in the shining straws of our corn fields-, and the canes and 

 bamboos of hotter climates ; and certain rough straws*, as that of the Equisetum 



hyemale, which is so rough as to be used in the 

 polishing of metals. It is also found in the 

 interior of the joints of certain bamboos, and 

 then is termed tabasheer, and from its rarity com- 

 mands a high price. It is also found in the hard 

 grains themselves, as- cf wheat and oats, and more 

 particularly of the rice; from which cause the 

 Caribs, the Malays, the South Australians, and 

 other savage nations have their teeth ground down 

 by the trituration of the uncooked grain. 



The layer is exceedingly thin, but yet it is- 

 one of pure flint, as may be proved by its non- 

 solubility in boiling nitric acid. It o-verlays the 

 vegetable tissue, and 

 assumes its form, 

 and therefore varies 

 greatly in appear- 

 ance, according to the object examined. 



In Fig. 98 we have an illustration of its appearance 

 in the common wheat. From this silex the flinty haira 

 of the oat arc formed ; and it is well known that animals 

 living much on oats are liable to intestinal accumu- 

 lations of these indigestible hairs ; and in a lesser degree 

 men eating oatmeal are liable to a like inconvenience. 

 The common meadow grass (Fe-stuca pratensis, Fig. 

 100), presents a silicious coating of considerable beauty. 

 The most beautiful examples are the Eqwsetum 

 ffyemale, the Pharus Cristatus (Fig. 101), the common rice (Oryza sativa), and the 

 stellate hairs of the Deutzia seabra (Fig. 102). 



It must be clearly understood that this substance constitutes no part of vegetable 

 structure, neither does 

 it assume any form of 

 organization, its sole 

 and most important 

 duty being to give 

 strength to the slender 

 stem, and to protect 

 the delicate tissues 

 from atmospheric in- 

 fluences. 



That the quantity 

 101. Silica in square and star- required to supply the 



wants of a field of corn Fip. 102 Sinous cells and stellate 

 is .cry considerable, %%. ^ k * "' * 

 may be proved from the following table ; and tbe more 



Fig. 100. Cups of Silica on the 

 chaff or palese of the common 

 meadow grass (Festucu pra- 

 ten&is.) 



