LEAVES OF PECULIAR FORMS AND USES. 



105 



How much the common American pitcher plants depend for 

 nourishment on the drowned insects in the pitchers is not 

 definitely known, but it is certain that some of the tropical 

 species require such food.^ 



In other rather common plants, the sundews, insects are 

 caught by a sticky secretion which proceeds from hairs on 

 the leaves. In one of the commonest sundews the leaves 

 consist of a roundish blade, borne on a moderately long 

 petiole. On the inner surface and round the margin of the 

 blade (Fig. 93) are borne 

 a considerable number of 

 short bristles, each ter- 

 minating in a knob which 

 is covered with a clear, 

 sticky liquid. When a 

 small insect touches one 

 of the sticky knobs, he is 

 held fast and the hairs at 

 once begin to close over 

 him, as shown in Fig. 

 94. Here he soon dies 

 and then usually remains 

 for many days, while the 

 leaf pours out a juice by 



which the soluble parts of the insect are digested. The 

 liquid containing the digested portions is then absorbed by 

 the leaf and contributes an important part of the nourish- 

 ment of the plant, while the undigested fragments, such as 

 legs, wing-cases, and so on remain on the surface of the leaf 

 or may drop off after the hairs let go their hold on the 

 captive insect. 



Fig. 94. — TiCaves of Sundew. (Slightly magni- 

 fied.) 

 The one at the left has all its tentacles closed 

 over captured prey ; the one at the right has 

 only half of them thus closed. 



1 Where the Sarra^enia is ahundant it "will he found interesting and profitahle to 

 make a careful class study of its leaves. See Geddes, Chapters in Modem Botany, 

 Chapters I and II, 



