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Show 18 DROSERA ROTUNDIFOLIA. CHAP. I. sphagnum moss grows ' and mosse.s depend altogether on t h e a t mosp here for their nounshment. Althou. gh the leaves at a hasty glance do not appear green, owing to the urple colour of the tentacles~ yet the upp r and lower spu rf :a ces of the blade ' the .p edicels of the central tentacl es, an d the petioles contain chl·o ro·1p hyll, so bt ha·t , no· ad ou bt, th e Plant obtains and assimi at· ,, s c· ar onhi c aci f rom th e ai·r · Nevertheless, consiu rin. g t e t Of the soil where it grows, the supply of nitroo-en na ure · d fi · 1 ld b xtremely limited, or quite e Ciont, un ess wou e e . . h' · t the plant had the powe~ of obtaining t Is Impor ant e l emen t f rom Captured Insects · We can thus under-stand how it is that the roots are so poorly deve~oped. These usually consist of only two o~ thr .e slightly divided branches, from half to one Inch In l ngth, furnished with absorbent hairs. It appears, therefore, that the roots serve only to imbibe water ; t~ou gh, no doubt, they would absorb nutritious matter 1f present · n the soil · for as we shall hereafter see, they absorb ~ weak sol~tion of carbonate of ammonia. A pl~nt of Drosera with the edges of its leaves curled Inwards so ~s to form a temporary stomach, with the gland~ of the closely inflected .tentacles p.ouring forth their acid secretion, which dissolves animal matter, afterwards to be absorbed, may be said to f ed ljke an animal. But, differently from an animal, it drinks by means of its roots; and it must drink larg ly, so as to retain many drops of viscid fluid round the glands, sometimes as many as 260, exposed during the whole day to a glaring sun. t.) CHAP. II. INFI,ECTION INDIRECTLY CAUSED. 19 CHAPTER II. THE MOVEMENTS OF THE TENTACLES FROM THE CONTACT OF SOLID BODIES. Inflection of the exterior t entacles owing to the glands of the di ·c being. excited by repeated touches, or by objects left in contact witk them-Difference in the action of bodies yielding and not yielding soluble nitrogenous matter-Inflection of the oxterio 1 · tentacles directly caused by objects left in contact with their glands - Perio<lH of commencing inflection and of subsequent reexpansion - Extreme minuteness of the particles causing inflection -Action under water-Inflection of tho exterior tentacles when their glands are excited by repeated touches- Falling drops of water do not cause inflection. I WILL give in this and the following chapters some of the many experiments made, which best illustrate the manner and rate of movement of the tentacles when excited in various ways. The glands alone 'i n all ordinary cases are susceptible to excitement. When excited, they do not themselves move or change form, but transmit a motor impulse to the bending part of their own and adjoining tentacles, and are thus carried towards the centre of the leaf. Strictly speaking, the glands ought to be called irritable, as the term sensitive generally implies consciousness; but no one supposes that the Sensitive-plant is conscious, and as I have found the term convenient, I shall use it without scruple. I will commence with the movements of the exterior tentacles, when indirectly excited by stimulants applied to the glands of the short tentacles on the disc. The exterior tentacles may be said in this case to Le indirectly excited, because their own glands are not directly acted on. The stimulus proceeding from the glands of the disc acts on the bending part of the . c 2 |