188 SOME BRITISH PLANT GROUPS 
ably by the addition to its diet of this animal food. 
When digestion is completed, the tentacles open again 
and prepare for a fresh victim. While the details of 
this remarkable process have been worked out only 
by careful and minute research in the laboratory, the 
main movements may be watched by anyone on any 
British moorland; or, bringing home a few plants in 
the damp moss in which they grow, we may amuse 
ourselves by experiments in feeding them. 
In comparison with the Sundews, the other insect- 
ivorous plants which are included in the British flora 
are of less interest. The Butterworts (Pinguicula), of 
which four species are known in these islands, have a 
rosette of smooth, broad, yellowish leaves covered 
with glands which exercise the same functions as 
those of Drosera. To the touch of raindrops, sand- 
grains, or other inorganic substances they are indif- 
ferent; but a tiny insect alighting on the sticky leaf at 
once provokes an outpouring of secretion, while the 
leaf rolls inward from the edges till the victim is 
securely caught; it is then digested as in the Sundew. 
The Bladderworts (Utricularia), of which several 
species may be found floating in boggy pools, are 
rootless, limp plants with finely divided leaves, among 
which are numerous little bladders (in reality strangely 
modified leaflets), and upright stems bearing pretty 
yellow Snapdragon-like flowers. The bladders do not 
help the plant to float, and appear to have for their 
sole function the securing of animal food. In the 
Common Bladderwort (U. vulgaris) they are about 
io inch long. At the upper end is a little hinged door, 
which is kept closed as by a spring against a thickened 
rim or door-frame. Outside the door are a few stiff 
