SECT. II 



PHYSIOLOffY 



229 



effected by the sudden closing together of the two halves of the leaf (Fig. 199). 

 This action is specially due to the irritability of three bristles on the upper 

 side of each half of the leaf (the leaf surfaces themselves are much less sensitive). 

 Upon the death of the insect, a copious excretion of digestive sap takes place 

 from glandular hairs on the leaf surface, followed by the absorption of the 

 products of the digestive solution. In the case of other well-known insectivorous 

 plants {JVcpent/ies, Ce2)halotus, Sarracenia, DarUngtonia), the traps for the 

 capture of animal food are formed by the leaves which grow in the shape of 

 pitchers (Figs. 46, 200). These trap-like re- 

 ceptacles are partially filled with a watery i-- 

 fluid excreted from glands on their inner sur- 

 faces. Enticed by secretions of honey to the 

 rim of the pitcher (in the case of Nepenthes), 

 and then slipping on the extraordinarily smooth 

 surface below the margin, or guided by the 

 downwardly-directed hairs, insects and other 

 small animals fall into the fluid and are there 

 digested by the action of ferments and acids. 

 The larvae which Clauthiau found living in 

 Ne'penthes pitchers, may, like intestinal para- 

 sites, be enabled to live there by secreting a 

 protective anti-ferment. In Sarracenia and 



FxG. I!i9.— A leai of D'lotiaea muacip^ila, sliowing the 

 sensitive bristles on its upper surface, which, in the 

 parts shaded, is also thicl?ly heset with digestive 

 glands. (After Darwin^ x 4.) 



Fid. 2C0.— Pitchered leaf of a 

 Nepenthes. A portion of the 

 lateral wall of the pitclier has 

 beenrenioved in order to show 

 the fluid {¥), excreted by the 

 leaf-glands, (h nat. size.) 



Cephalotus, Goebel was unable to discover any digestive ferments ; but in 

 Cephalotus it was possible to determine that the secretions have antiseptic 

 properties. 



In relation to insectivorous plants certain phanerogamic parasites {^^) 

 may be considered which were omitted above (p. 226) since they 

 possess green leaves and are evidently autotrophic as regards their 

 supply of carbon. In spite of this, however, the plants only develop 

 normally, when their root system is in connection with .the roots of 

 other plants by means of disc-shaped haustoria. They may even (as 

 is also the case with Cuscnta) enter into this relation with other 

 individuals of the same species. Thesimn, belonging to the Santalaceae, 



