CARNIVOROUS PLANTS 135 



we shall see that the bright, conspicuous colour possesses a very con- 

 siderable value in attracting insects ; and in the case of the pitcher-plant, 

 too, the gorgeous colour probably allures insects to settle on the rim of 

 the pitcher, and they are tempted to dally the longer since it secretes 

 honey. But the thick, swollen rim of the pitcher is as smooth as if it 

 were made of polished wax, and resembles the petals of those 

 magnificent large orchids, the Stanhopeaa ; the inner surface of the 

 pitcher below the margin is also smooth, so that insects which creep 

 about seeking honey are apt to slip and fall to the bottom. Even if 

 many of them are not at once killed by the digestive fluid, but are able 

 to climb up the smooth wall again, they cannot escape, for beneath 

 the swollen rim, which projects inwards, there is a circle of strong 

 bristles or teeth, with the points directed downwards, which, like 

 thorns, prevent the captive's escape. Thus the pitchers of Nepenthes 

 secure and digest a large number of insects, and we can easily under- 

 stand that the plant acquires a considerable amount of valuable 

 nourishment in this way, for ready-made protoplasm is a convenient 

 food to which the plant has to do but little in order to convert it into 

 its own particular kind of living matter. 



The toothwort (Lathrcm squamaria) must also be briefly noticed 

 here, because it does not catch insects through the medium either of 

 air or of water, but through the earth. As is well known, this plant 

 is parasitic on the roots of various foliage-trees. It is of a pale 

 yellowish colour, and has no green assimilating parts. For such 

 a plant it must be of particular value to be able to catch animals and 

 to use them as food. To this end the short, pale leaves, which 

 surround the creeping, underground stem in the form of closely 

 appressed scales, have been modified into snares for minute animals. 

 The leaves have their upper parts recurved downwards, and the edges 

 have grown together, so that only a small opening is left at the base, 

 and this leads into a system of tunnels. Aphides, rotifers, bear- 

 animalcules, but especially springtails (Podurids), creep into these 

 hollow leaves, are held fast by a sticky secretion, and are dissolved 

 and absorbed. 



Another example, also indigenous, is that graceful marsh plant, 

 the butterwort (Pinguicula vulgaris), whose broad, tongue-shaped 

 leaves, arranged in the form of a rosette, have been modified into an 

 insect trap by the turning up of their edges, while the middle is 

 deepened into a longitudinal groove (Fig. 25). The whole upper 

 surface of the leaf is covered with an enormous number of little 

 mushroom-shaped glands {B, C, Dr), which secrete a viscid slime. 

 Insects which settle on the leaf stick fast, and as the glands continue 



