184 PLANTS OP NEW ZEALAND 



and, if the insect is large, the whole leaf becomes more or less 

 concave, and large quantities of juice are poured out from the 

 glands. This juice is in many ways similar to the human 

 gastric fluid, and accomplishes the same purpose, for, after 

 several days, the insect is digested, and little of it is left, except 

 the wings and horny casing. The leaf then gradually opens 

 out, and, after a day or two, is again in a position to capture 

 insects. The sensitiveness of the tentacles is marvellous. 

 Thus, it has been said, that the four-thousandth part of a 

 milligram of ammoniun carbonate is sufficient to produce 

 motion in them, while a piece of a woman's hair about two- 

 tenths of a millimetre (i.e. less than one-hundredth of an inch 

 in length), placed upon a gland, also caused inflection in the 

 filament belonging to the gland. The above description deals 

 chiefly with D. rotundifolia, an English and continental plant. 

 To it alone, Darwin devoted 270 pages of his book ; but he 

 also experimented on two Australasian species D. spathulata 

 and D. binata. He found that functionally they differed little 

 from D. rotundifolia. Both these species occur in New Zealand, 

 though Darwin's specimens came from Australia. The very 

 handsome D. binata, in particular, interested him very much. 

 He refers to it as "this almost gigantic Australian species." In 

 it the bifurcated leaf -blade, which is very long and narrow, is 

 itself in no case inflected. Glands are borne, not only at 

 the ends of the tentacles in this species, but " on both upper 

 and lower surface of the blade, there are numerous minute, 

 almost sessile glands, consisting of four, eight, or twelve 

 cells." There are also on the backs of the leaves of this 

 species, a few tentacles near the margins. These tentacles 

 are remarkable in possessing no power of motion, but 

 even had they this power, they are generally too short to 

 bend round to the upper surface of the leaf. In their 

 present situation, they seem to be of little use ; and Darwin 

 regards these and the sessile glands, as vestigial structures, 

 which have been lost in other species of the genus. 



*Darwin "Insectivorous Plants," p. 282. 



