6i8 



ECOLOGY 



Besides the various species of Drosera, other members of the same family, as 

 Drosophyllum, have irritable glandular hairs. Two of the most remarkable genera 

 are Aldrovanda and Dionaea, which have sensitive leaf blades that close suddenly 

 when irritated, and prevent the escape of alighting insects (figs. 657-659). Im- 

 pact upon the stiff outer part of certain hairs is perceived by delicate cells beneath 

 and transmitted to the region where movement is effected. The secretion of 

 digestive fluids, and subsequent digestion and absorption 

 take place as in Drosera. 



Pitcher plants. The pitcher plants (Sarracenia, Nepen- 

 thes, etc.), like Drosera, commonly are bog plants. The 

 pitcher-like leaf blades of Sarracenia (fig. 908) are partly 

 filled with rain water, into which insects, by chance or 

 attracted by the bright colors, frequently wander and are 

 drowned. For crawling insects, entrance is easy and exit 

 difficult by reason of stiff downward-pointing hairs at the 

 edge of the pitcher. In Nepenthes (fig. 656) nectar is 

 secreted at the pitcher edge, doubtless forming an addi- 

 tional attraction. Proteolytic enzyms have been discovered 

 in the pitchers of Nepenthes, the glands occurring at the 

 base of cavities and consisting of spherical multicellular 

 structures, below which are the terminal tracheids of a 

 conductive bundle, as in Drosera. Enzym secretion prob- 

 ably does not occur in Sarracenia, though it is possible 

 that the products of insect decay may enter the plant, 

 much as in saprophytes. In Dischidia, an epiphytic 

 pitcher plant, there are double pitchers, one inside the 

 other; the outermost pitcher is a sort of living flower pot 

 in which earth and water collect and into which adventi- 

 tious roots penetrate from other parts of the plant. 



Butter-worts and bladder-worts. A third family of carniv- 

 orous plants is represented by the butterworts (Pinguicula) 

 and the bladderworts (Utricularia), which commonly inhabit 

 swamps or ponds. On the leaf blade of Pinguicula, as in 

 Drosera, there are glandular hairs that secrete viscous 

 substances, and the leaf margins, but not the hairs, also 

 incurve when alighting insects irritate the leaf. The hairs 

 are of two sorts; some with relatively long stalks hold fast 

 to the visiting insects, while shorter hairs, consisting of an 

 eight-celled disk with a hidden stalk, are thought to be more 

 The cells secrete enzyms only when the hairs are irritated. 

 The bladders of Utricularia have an opening at one end, within and about which are 

 a number of hairs and other structures which are so arranged as to prevent egress, 

 though permitting easy entrance, much on the principle of an eel-trap (figs. 909, 

 910). Minute water animals often crawl or swim into the bladders, where they 

 are detained. The presence of the imprisoned animals has led to a general belief 

 in their utilization by the plant, the forked hairs of the inner surface of the bladder 

 being supposed to play a part in the process, and there is some evidence of the 



FIG. 908. A leaf 

 of the pitcher plant 

 (Sarracenia purpurea) ; 

 usually such pitcher 

 leaves are partly filled 

 with water into which 

 insects often crawl or 

 fall. 



efficient in absorption. 



