THE PHYSIOLOGY OF PITCHER-PLANTS. 



Ill 



pitchers which are not " insect-traps " are both related to the 

 water-supply of the plant ; in Lathraea, the main use of the 

 pitcher seems to be to relieve the plant of the excess of 

 water which it may have absorbed ; whilst in Dischidia, on the 

 contrary, the main use of the pitcher is to husband to the utmost 

 the water-resources of the plant. 



It is remarkable that the pitcher form should have been as- 

 sumed by the leaves of so many different plants, some of which 

 are systematically far removed from each other, and that the 

 objects in view should be so widely different. Such considerations 

 naturally suggest the difficult question as to the origin and evolu- 

 tion of the pitchered leaf in the vegetable kingdom ; a question 

 to which, I will frankly admit, I cannot promise you a satisfactory 

 answer. Beccari (" Malesia," vol. i., p. 236, 1878 ; vol. ii., p. 252, 

 1886) has urged, whilst especially discussing Dischidia, that 

 pitchers are gall-formations, caused by the irritation set up by 

 insects, which have become hereditary because the plant has 

 found them useful for its own purpose ; but this theory has not 

 met with general acceptance. For my own part, I would ven- 

 ture to suggest that the origin of pitchers is to be traced back, 

 not to the action of some extraneous cause, but rather to some 

 special adaptation to meet the primary physiological needs of 

 plants growing under certain special conditions. To take first 

 the typical pitcher-bearing plants, such as the Sarraceniaceae, 

 Nepenthes, and Cephalotus : it is by no means probable that the 

 pitchers of these plants were developed at once into insect-traps 

 such as we know them to be ; for this end has been even more 

 successfully attained in quite other ways by such plants as 

 Drosera, Dionaea, &c. On the contrary, it is probable that these 

 pitchers had originally a different and a more primitive function. 

 All these genera grow in damp situations : hence it is not an 

 impossible conjecture that their pitchers may have been primarily 

 developed as organs for the excretion of excessive water, like 

 the pitchered scale-leaves of Lathraea ; but with this difference, 

 that whereas in Lathraea the water is poured out into the soil, 

 in these genera it was retained in the pitchers for subsequent 

 re-absorption, when necessary, a special provision of im- 

 portance in view of the fact that these plants are capable of 

 active transpiration under appropriate external conditions. 

 Insects, as a matter of course, came to be drowned in these 



