THE PHYSIOLOGY OF PITCHER-PLANTS. 



105 



be no doubt that it is an apparatus for catching insects, re- 

 sembling that of Nepenthes rather than that of Sarracenia. 



With regard to the properties of the secreted liquid, the 

 only evidence that it has any digestive power is a statement by 

 Lawson Tait, made at the Glasgow meeting of the British 

 Association, 1877 (quoted by Dickson in his paper on the 

 Structure of the Pitcher of Cephalotus, " Journ. Bot.," vol. 27, 

 new series, 1878), that the results of experiments performed 

 by him with fluid taken from unopened pitchers, were such as 

 to show that it exerted a digestive action upon animal sub- 

 tances similar to that exhibited by fluid from Nepenthes pitchers. 

 Goebel, on the contrary, as the result of his own observations, 

 takes the opposite view. He remarks, however, that the liquid 

 seems to exert a distinct antiseptic action ; so that whilst it is 

 probable that the disintegration of the captured insects is 

 effected by micro-organisms, it is a process, not of putrefaction 

 as in Sarracenia, but of digestion, a conclusion which seems 

 rather paradoxical. 



The pitchers which we have considered so far are all such 

 as may capture flying insects ; though Cephalotus, owing to the 

 fact that its pitchers are on the ground, captures more especi- 

 ally crawling insects. We come now to the consideration of 

 those pitchers which do not capture flying insects, but only 

 such small animals as either swim or crawl ; this section in- 

 cludes Utricularia (with its immediate allies Polypompholyx 

 and Biovularia) and Genlisea. The aquatic forms of Utricularia 

 capture swimming insects, Crustacea, &c. ; and the land-forms, 

 as also Genlisea, capture insects, &c, in the soil by means of 

 their subterranean pitchers. 



In speaking thus of Utricularia, I have anticipated some- 

 what ; for I have adduced no evidence to show that the " blad- 

 ders " of these plants really are insect- traps. It used to be 

 thought that the pitchers of the aquatic forms served as floats 

 to bring the plant to the surface at the time of flowering. 

 Thus De Candolle (" Physiol. Veget.," II., 1832) says :— " When 

 the plant is young, the bladders are filled with mucus which is 

 heavier than water ; hence the plant is kept at the bottom by 

 this weight. When flowering approaches, the root secretes air 

 which enters the bladders and expels the mucus, raising the 

 valve of the bladder ; then the plant, provided with a crowd of 



