ON THE IRRITABILITY OF VEGETABLES, p,"^ 



upper surface is covered with hairs, but when deprived of them 

 appears nearly like the under. The leaf itself is vervthin,and 

 may be folded in different directions without breaking. The 

 hairs, which cover the upper surface of the leaves, are of va- 

 rious lengths. Thosj on the margin are sometimes three 

 eighths of an inch long, while those in the centre are not 

 more than one line. In some well expanded leaves we may- 

 see nearly a regular gradation of the intermediate hairs be- 

 tween the two extremes. The marginal hairs are flattish at 

 their base, and of the same colour with the leaf itself, (in- 

 deed they seem to be merely continuations of it). The 

 other hairs are not so flat at their base as the marginal ones, 

 but are also of the same colour as the leaf. The long hairs, 

 except at their base, are of a red colour, each terminated by 

 a little knob ; while in the central hairs the knob is placed 

 immediately on the white part of each. Every hair then is 

 terminated by a little rounded body. In general each of 

 these knobs is covered by a transparent and viscid rluid, 

 which gives a fine appearance, and on account of which the 

 plant was denominated ros solis or sundew. Each of these 

 knobs appears to be a little gland, which secretes the viscid 

 fluid* for a purpose soon to be mentioned. 



The chief difference between the leaves of the longifolia j, n*leaved. 

 and the rotundifolia is in the shape, those of the former 

 being obovate. 



* This fluid, which covers the glands of the hairs (of the leaves) of p-j^ f d, - 

 the indigenous species of drosera, has been differently denominated, sera. 

 Darwin talks of the pellucid drop of mucilage on every thread of the 

 fringe, and in the same page speaks of the globules of mucus. Bot. 

 Gard. Roth calls it the clammy juice, and 1 have here called it a trans- 

 parent viscid fluid. This juice covers the glands when under the influ- 

 ence of the hottest sun; and also during the wettest weather. When p res erits a 

 the leaf is put under the electrical influence, each little globule of fluid beautiful 

 spins out like a small tree, presenting a fine appearance. This fluid pearancewhea 

 seems fo possess the following properties, although I cannot vouch for 

 the accuracy of the experiments. It is transparent, insipid, rather more b P r0 P eu 

 consistent than the albumen ovi, exti. mely te cious, insoluble in wa- 

 ter, soluble in alcohol, in diluted sui, huric acidj d in • ,.i.:ion of po- 

 tash, is not very combustible, and is an electric or no, conductor. Quere. 

 Is it a fluid sui generis? It certainly deserves the atteatiou of the che- 

 mist. 



The 



