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Show 344 GLANDULAR HAIRS, CHAP. xv. -sessile ones arra!lged in ro':s, and others supported on moderately long ped1cels. . Towards the narrow summits of the leaves the ped1cels are longer than elsewhere, and here equal the diameter of the leaf. The glands are purplish, much fl atteneJ, and formed of a single layer of radiating cells, which in the larger glands are from forty to fifty in nu1nber. The pedicels consist of single elongated cells, with colourless, extremely delicate walls, marked with the finest intersecting spiral lines. vVhether these lines are the result of contraction from the drying of the walls, I do not know, but the whole pedicel was often spirally rolled up. Those glandular hairs are far more simple in structure than the so-called tentacles of the preceding genera, and they do not differ essentially from those borne by innumerable other plants. The flower-peduncles bear similar glands. Tho most singular character about the leaves is that the apex is enlarged into a little knob, covered with glands, and about a third broader than the adjoining part of the attenuated leaf. In two plac s d ad flies adhered to the glands. As no instance is known of unicellular structures having any power of movement,* Byblis, no doubt, catches insects solely by the aid of its viscid secretion. These probably sink down besmeared with the secretion and rest on the small sessile glands, which, if we may judge by the analogy of Drosophyllum, then pour fourth their secretion and afterwards absorb the digested matter.· Supplementary Observations on the Power of· Absorption by the Glandular Hairs of other Plants.-A few observations on this subject may be here conveniently introduced. As the glands of many, probably of all, * Sachs,' Traite de Bot.' 3rd edit. 1874, p. 1026. CHAP. xv. THEIR POWER OF ABSORPTION. 345 the species of Droseracere absorb various fluids or at least allow them readily to enter,* it seemed desirable to ascertain how far the glands of other plants which are not specially adapted for capturing insects, had the same power. Plants were chosen for trial at hazard, with the exception of two species of saxifrage, which were selected from belonging to a family allied to the Droseraceoo. Most of the experi1nents were made by immersing the glands either in an infusion of raw meat or more commonly in a solution of carbonate of ammonia, as this latter substance acts so powerfully and rapidly on protoplasm. It seemed also particularly desirable to ascertain whether ammonia was absorbed, as a small amount is contained in rainwater. With the Droseraceoo the secretion of a viscid fluid by the glands does not prevent their absorbing; so that the glands of other plants might excrete superfluous matter, or secrete an odoriferous fluid as a protection against the attacks of insects, or for any other purpose, and yet have the power of absorbing. I regret that in the following cases I did not try whether the secretion could digest or render soluble animal substances, but such experiments would have been difficult on account of the small size of the glands and the small amount of secretion. We shall see in the next chapter that the secretion from the glandular hairs of Pinguicula certainly dissolves animal matter. Sr~xifraga umbrosa.-The flower-peduncles and petioles of the leaves are clothed with short hairs, bearing pink-coloured glands, formed of several polygonal cells, with their pedicels divided by partitions into distinct cells, which are generally colourless, but sometimes pink. The £;lands secrete a yellowish viscid fluid, by * The distinction between true absorption and mere permeation, or imbibition, is by no means clearly understood: see Miiller's 'Physiology,' Eng. translat. 1838, vol. i. p. 280. |
