DROSERACE^ 



203 



ment. Such a particle would have been entirely 

 imperceptible on the tip of tlie tongue, which is the 

 most sensitive part of our organisation. Of many 

 stimulants tried carbonate of ammonia was the most 

 energetic. A dose of tsAtfo of a grain given to a 

 gland produced a marked effect. On the other hand, it 

 is remarkable that though so sensitive the tentacles 

 do not move if struck by drops of rain, even if coming 

 down heavily. Inorganic sub- 

 stances again, such as bits of 

 glass, or sand, or organic sub- 

 stances not containing nourish- 

 ment, produce little effect, or if 

 the tentacles bend slightly over 

 them they seem soon to find 

 out their mistake. 



It seems wonderful indeed 

 how such remarkable contriv- 

 ances can have originated. 

 Nevertheless some light appears 

 to be thrown on the problem if 

 we bear in mind that we find 

 every gradation. Many plants 

 produce a sticky secretion, 

 which apparently seems only to 

 prevent creeping insects from 

 ascending the plant and eating the leaves or robbing 

 the flowers of nectar. In others, as, for instance, 

 Saxifraga tridactylites and S. umbrosa, insects are 

 not only occasionally captured, but apparently sucked 

 of their juices. In Drosera, and, as we shall see, 

 in Pinguicula, the contrivances are more elaborate ; 

 and perhaps to this the great success of the genus in 

 the struggle for existence may be due, for there are 

 many species, spread almost over the whole continental 

 world. 



D. anglica. — The leaves of this species stand erect, 

 and, as is usual in such cases, are not suddenly widened 

 at the end. 



Fig, 



140. — Drosera roiuniliJ'oUa. 

 Leaf enlarged, with the tenta- 

 cles on one side inflected over a 

 bit of meat placed on the disk. 



