VEGETATION OF STILL WATER 33 



which the insect is caught. The tentacles, as already described, 

 bend over, the leaf curves over, and the animal is digested by the 

 juice secreted by the gland of the 

 tentacle. 



Another insectivorous plant that 

 performs movements by which in- 

 sects are entrapped is the Butter- 

 wort, which thrives on damp spots, 

 the neighbourhood of springs, banks 

 of brooks, peat-bogs. Very often 

 it is found in company with the 

 Sundew. The Butterwort has its 

 leaves to some extent permanently 

 incurved ; insects washed down by 

 the rain are thus caught by these 

 incurved margins. The leaves are 

 covered with two sets of glands, 

 which secrete mucilage and an acid 

 digestive fluid. It has been calcu- 

 lated that there are 25,000 muci- 

 lage secreting glands on a square 



,. P -,-> ir FIG. 10. Sundew (Drosera anglica). 



centimetre of a Butterwort leaf, 



and that six to nine leaves will have about half a million of them. 

 The body of the insect is digested by the acid juice. It has been 

 found by experience that inorganic material, such as grains of 

 sand, do not stimulate the secretion of either the mucilage or the 

 digestive acid. The Butterwort bears slender flower stems, each 

 with a single two-lipped purple flower, which is spurred. The 

 Butterwort bears transplanting very well, and will flower in a 

 window box, provided it is on the shady side of the house and 

 that the soil is kept moist with bog-moss. The number of insects 

 that these plants will catch is almost incredible. Darwin relates 

 that 142 insects were found on thirty-two leaves, which had also 

 entrapped leaves of such plants as Heather, Sedges, and Rushes. 

 The insects included small flies, some ants, a few small beetles, 

 spiders, and even small moths. 



Another feature of most bog plants is their xerophytic char- 

 acter, perhaps owing to the fact that the peat-water can be 



VOL. V. 3 



