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strengthened by a copious deposit of silica or flint-earth, lodged in 

 the cells of its cuticle or skin. The quantity of this substance is 

 often sufficient to maintain the form of the part to which it ap- 

 pertains, when all the vegetable matter has been removed by 

 burning, or otherwise ; a circumstance well known to microscopic 

 observers, who obtain by so doing beautiful objects for polarization. 

 The earth in question is elaborated from the soil by the roots of 

 the plant, being probably retained in its nutritive juices in a fluid 

 state through its affinity with potash, as a silicate of that alkali. 

 The hardness of the exterior of the fruit or grain, which in some 

 instances equals that of agate, as in that of Coix Lachryma, an 

 East Indian grass, called from its form and pearly lustre Job's- 

 tears, is due to a similar deposit. The silica is frequently lodged 

 in considerable quantity in the joints or nodes of the stem, con- 

 tributing greatly to strengthen that of the larger kinds ; and in 

 the Bamboos it often finds its way into the hollows above them, 

 probably through perforations made by insects, where it consti- 

 tutes the substance called in Persia and India tdbasheer. The 

 vitrified matter left by the burning of corn and hay-stacks, is due 

 to this necessary element of grass-composition ; a fact capable of 

 demonstration by subjecting the ashes of almost any grass-stem to 

 the action of the blow-pipe, under which globules of glass may be 

 obtained, varying in hue according to the species employed ; that 

 from Wheat-straw being colourless, and, if properly managed, 

 transparent ; while the straw of Barley yields it of a brilliant topaz- 

 yellow, and that of the Oat of a pale straw-colour; — the hue, how- 

 ever, is not, judging from my own experience, to be depended upon, 

 as I have several times obtained a perfectly colourless globule from 

 Barley-straw. The result is probably dependent upon accidental 

 circumstances. 



The aggregate value of the Grasses, as afi^ording the principal 

 food of herbivorous animals, especially of those in the subsistence 

 of which we are the most interested, is greatly enhanced by the 



