_Thirdly_. The epidermis, subjected to chemical analysis, had all the properties of silex. _Fourthly_, The similar appearance of the epidermis of reeds, corn, and grasses, induced me to suppose that they also contained silex. By burning them carefully and analyzing their ashes, I found that they contained it in rather larger proportions than the canes. _Fifthly_. The corn and grasses contain sufficient potash to form glass with their flint. A very pretty experiment may be made on these plants with the blowpipe. If you take a straw of wheat, barley, or hay, and burn it, beginning at the top, and heating the ashes with a blue flame, you will obtain a perfect globule of hard glass, fit for microscopic discovery." The circumstance, that all canes, as well as straws and hollow grasses, have an epidermis of silex, is one of the most singular facts in nature. Mr. Davy, in another place, has stated the advantages arising to this class of vegetables, from their stony external concretion: namely, "the defence it offers from humidity; the shield which it presents to the assaults of insects; and the strength and stability that it administers to plants, which, from being hollow, without this support, would be less perfectly enabled to resist the effect of storms. Those canes which are not hollow, are long and slender, and from wanting the power to sustain themselves, come usually in contact with the ground, when they would speedily decay, from moisture, but from the impenetrable coat of mail with which nature has furnished them. But questions still arise for future investigators. How came the matter of flint to invest those plants which most need it, and not others? Whence does this silex come? Is it derived from the air, or from water, or from the earth? That it emanates from the atmosphere is wholly inadmissible. If the silex proceed from water, where is the proof? and how is the superficial deposit effected? Also, as silex is not a constituent part of water, if incorporated at all, it can be held only in solution. By what law is this solution produced, so that the law of gravity should be suspended? If the silex be derived from the earth, by what vessels is it conveyed to the surface of the plants? and, in addition, if earth be its source, how is it that earth-seeking, and hollow plants, with their epidermis of silex, should arise in soils that are not silicious? being equally predominant, whether the soil be calcareous, argillaceous, or loamy. The decomposition of decayed animal and vegetable substances, doubtless composes the richegt superficial mould; but this soil, so favorable for vegetation, gives the reed as much silex, but no more, in proportion to the size of the stalk, than the same plants growing in mountainous districts, and primitive soils. It is to be regretted, that the solution of these questions, with others that might be enumerated, had not occupied the profoundly investigating spirit of Mr. Davy; but which subjects now offer