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Show 354 GLANDULAR HAIRS. CHAP. XV. The aggregating proeess s~reads from the glands do,vn the pedicels of the haus ; and w_e 1nay assume that any matter which is absorbed ultimately roaches the tissues of the plant. On the other ha~cl, the process t rave1 s . up the hac l. rs w· henever a surface IS. en t .a nd ex-posed to a solution of the carbonate of ammonia. The glands on the flower- stalks and. leaves of Primula sinensis; quickly. absorb a solution_ of the carbonate of ammonia, and the protoplasm which they con t ai" n becomes aob·ba regated. rrhe proc. ess was seen in son1e cases to travel from the glands Into the upper cells. of the pedicels. Exposure· for 10 n1. to _the v.a Po,u of this salt likewise induced aggregatiOn. L • When leaves were left from G hrs. to 7 hrs. In a sti~ong solution. or were long exposed to the vapour, tho httle masses. ~f protopla&In became disi~tegratecl, ~row1~, and. granular, and ·were apparently lnllecl. An InfusiOn of raw meat produced no effect on the glands. . The lin1pid contents of the gla~cls of Pelargon~um zonale became cloudy and granular In from 3m. to 5 m. when they were im1nersed in a weak solution of the carbonate of am1nonia; and in the course of 1 hr. granules appen.red in the upper cells. of the po~licels. As the aggregated masses slow 1 y changed then forms, a1:d as they suffered disintegration when left for a. considerable tin1e in a strong solution, th re can be httle doubt that they consisted. of protoplasm. It is doubtful whether an infusiion of raw n1eat procllll.cecl any effect. The alandular hairs. of Ottdinary plants have gene· rally b:en considered by physiologists to serve only as secreting or excreting organs, but we now know t~at they have the power, at least in so1ne cases, _of absorbi~g both a solution and the vapour of aminonia. As ramwater contains a small percentage of a1nmonia, and t~e atn1osphere a 1ninute quantity of the earbonate, this CHAP. XV. DROSERACEJE. 355 po.wer can hardly fail to be beneficial. Nor can the benefit be quite so insignificant as it might at first be thought, for a moderately fine plant of Primula sinensis bears the astonishing number of above two millions and a half of glandular hairs,* all of which are able to absorb ammonia brought to them by the rain. It is moreover probable that the glands of some of the above named plants obtain animal matter from the insects which are occasionally entangled by the viscid secretion. CoNCLUDING REMARKS ON THE DROSERACEJE. The six known genera composing this family have now been described in relation to our present subject, as far as my means have permitted. They all capture insects. ~rhis is effected by Drosophyllu1n, Roridula, and Byblis, solely by the viscid fluid secreted from their glands ; by Drosera, through the same means, together with the movements of the tentacles; by Dionrea and Aldrovanda, through the closing of the blades of the leaf. In these two last genera rapid * My son Francis counted the hairs on a space measured by means of a micrometer, and. found that there were 35,336 on a square inrh of the upper surface of a leaf, and 3U,O;i5 on the lower surf~ce; that is, in about the propol'twn of lOU on the uppm· to 85 ?n the lower surface. On a square mch of both surfaces there were 65,371 hairs. A moderately fine plant bearing twelve leaves (the larger ones beino- a little more than 2 inches in ° diameter) was now selected, and the area of all the leaves, together with their fo~t-st~lks (the flower-stems not bemg mel uded), was found by a planimeter to be 39·285 square inches; so that the area of Loth surfaces was 78 ·57 square inches. Thus the plant (excluding the flower-stem::;) must have borne the astonishing number of 2,56s,089 glandular hairs. 'rl10 hairs were counted late in the autumn, and by the following spring (May) the leaves of some other plants of the same lot were found to be from one-third to onefourth broader and longer than tl1ey were before ; so that no doubt the glandular hairs had increased in number, and prcbably now much exceeded three millions. ~ .\ 2 |