viii] 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^. Experimental work 

 has also demonstrated that treat- 

 ment with ammonium nitrate, 

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

 tion has occurred^. 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^. 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 



1 Goebel, K. (i 891-1893). 2 Darwin, C. (1875). 



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

 P- 365. 



Fig. 62. Utricularia Bremii, Heer. 



Part of leaf with bladder. (Enlarged.) 



[Meierhofer, H. (1902).] 



