vm] CARNIVOROUS HABIT 95 



Utricularias do, as a matter of fact, catch animals in their 



utricles, but the questions still remain whether the absorption 



of organic material actually takes 



place, and, if so, whether the 



carnivorous habit is of definite 



benefit to the plant. The inner 



epidermis of the bladders is cuti- 



cularised except as regards the 



four-armed hairs (Fig. 61, p. 93) 



which are thin-walled. These 



hairs, in the case of a bladder 



enclosing decaying animals, have 



been seen to include oil-drops, 



which may be presumed to be 



derived from the animal tissues, 



since the hairs in a bladder which 



had received no food, showed no 



such drops 1 . Experimental work 



has also demonstrated that treat- 



ment with ammonium nitrate, 



etc., produces changes in the hairs which suggest that absorp- 



tion has occurred 2 . These observations would not be sufficient 



in themselves to prove that the entrapped animals serve as 



a source of food for the plant, but a demonstration of this 



point was supplied by certain comparative cultures of Utri- 



cularias growing in water with or without animal life. From the 



upshot of these experiments it appeared that the plants deprived 



of animal food only showed about one-half of the growth 



of those that were allowed to catch their prey in the normal 



way 3 . A further problem which presents some difficulty is 



that of the causes which bring about the death and absorption 



of the entrapped animals. No highly poisonous substance 



can be present in the bladders, since the imprisoned animals 



FIG. 62. Utricularia Bremii, Heer. 



Part of leaf with bladder. (Enlarged.) 



[Meierhofer, H. (1902).] 



1 Goebel, K. (1891-1893). 



2 Darwin, C. (1875). 



3 Biisgen, M. (1888). See also Darwin, C. (1888), footnote to 



