136 



THE EVOLUTION THEORY 



to pour out more and more slime, while at the same time the edges of 

 the leaf, stimulated by the struggling of the insect, curl over still 

 farther, the victims are drowned in the slime, and ultimately 

 absorbed ; for this secretion is so powerful that even fragments of 

 cartilage are dissolved by it in forty-eight hours. Midges and may- 

 flies in particular fall victims to this plant, which is common in 

 marshy places both in mountain and plain. 



We must also mention the sundew (Drosera rotund if olia), which 



Fig. 25. Butterwort {Pinguicula vulgaris). A, the entire plant, showing the 



incurved margins of the leaves and some insects caught by the secretion 

 section through a leaf, enlarged 50 times, r, the margin 



B, cross- 



glands. 



C, a portion of the leaf-surface, magnified 180 times. 



Dr, Dr\ the two kinds of 



takes its name from the seeming dewdrops that sparkle in the sun on 

 the leaves, or rather on the rounded extremities of long and rather 

 thick cilia-like hairs which cover the whole upper surface of the leaf. 

 In reality the apparent dewdrops consist of a sticky, clear, viscid 

 slime, which is secreted by the glandular ends of the pin-shaped hairs 

 or * tentacles.' Insects which settle on the leaf are caught by the 

 slime, and in this case also an acid, pepsin-containing fluid is secreted, 

 which gradually effects the digestion of the soluble parts of the insect. 

 It is especially noteworthy that it is not only those tentacles which 



