| OCR Text |
Show 76 DROSERA ROTUNDIFOLIA. CHAP. v. . CHAPTER V. THE EFFECTs oF NoN-NITROGENous AND NITROGENous ORGANIC FLums ON THE LEAVES. Non-nitro()'enous fluids -Solutions of gum arabic- Sugar- Starch -Dih~ted alcohol-Olive oil-Infu ion and decoction of teaNitrogenous fluids~ Milk- Urine- Liquid album n-Infn ·ion of raw meat-Impure mucus -Saliva -Solution of i. ·ingla ·sDifference in the action of these two sets of fluids- Decoction of green peas- Decoction and infusion of cabbage- Decoction of grass leaves. WHEN, in 1860, I :first observed Drosera, and was led to believe that the leaves absorbed nutritious 1natter from the insects which they captured, it seemed to me a good plan to make some preliminary trials with a few common fluids, containing and not containing nitrogenous matter; and the results are worth giving. In all the following cases a drop was allowed_ to fall from the same pointed instrument on the centre of the leaf; and by repeated trials one of these drops was ascertained to be on an average very n arly half a minim, or 9 J 0 of a fluid ounce, or ·0295 ml. But these measurements obviously do not pretend to any strict accuracy; moreover, the drops of the viscid flui ls w re plainly larger than those of water. Only one leaf on the same plant · was tried, and the plants were collected from two distant localities. The experiments were made during August and September. In judging of the effect~, one caution is necessary: if a drop of any adhesive fluid is placed on an old or feeble 1 af, the glands of which have . ceased to secrete copiously, the drop sometimes dries up, ·especially if the plant CIIAP. v. EFFECTS OF ORGANIC FLUIDS. 77 is kept in a room, and some of the central and submarginal tentacles are thus drawn together, giving to them the false appearance of having become inflected. This sometimes occurs with water, as it is rendered adhesive by mingling with the viscid secretion . Hence ihe only safe criterion, and to this alone I have trusted, is the bending inwards of the exterior tentacles, which have not been touched by the fluid, or at most only at their bases. In this case the movement is wholly due to the central glands having been stimulated by the fluid, and transmitting a motor impulse to the exterior tentacles. The blade of the leaf likewise often curves in wards, in the same mannet as when an insect or bit of meat is placed on the disc. This latter movement is never caused, as far as I hav.e seen, by the mere drying up of an adhesive fluid and the consequent drawing together of the tentacles. First for the non-nitrogenous 'fluids. As a preliminary trial, drops of distilled water were placed on between thirty and forty leaves, and no effect whatever was produced; nevertheless, in some other and rare cases a few tentacles became for a short time in- fleete' d; but this may have been caused by the glands having been accidentally touched in getting· the leaves into a proper position. That water should produce no effect might have been anticipated, as otherwise the leaves would have been excited into movement by every shower of rain. Gum arabic.-Solutions of four degrees of strength were made; one of six grains to the ounce of water (one part to 73); a second rather stronger, yet very thin; a third moderately thick, and a fourth so thick that it would only just drop from a pointed instrument. These were tried on fourteen leaves; the drops being left on the discs from 24 hrs. to 44 hrs.; generally about |
