ZOO CLIMBERS, PARASITES, SAPROPHYTES. 



Further information regarding the work of soil-Bacteria is given in 

 Plant Biology, Chap. III. (" Roots and their Work") and Chap. X. 

 ("Biology of the Soil"). 



241. Carnivorous or Insectivorous Plants obtain part 

 of their nitrogenous food by catching insects in various ways, 

 by means of modified leaves, and afterwards absorbing the 

 soft parts of the insects. The British insectivorous plants 

 are the Sundews, Butterwort, and Bladderwort. 



The Butterwort (Pinguicula) has a basal rosette of broad 

 leaves, whose upper surfaces are covered with sticky glands, 

 while the margins are rolled inwards slightly. Small insects 

 are caught by the sticky liquid and washed by rain to the 

 edge of the leaf, which curls inwards and encloses them ; the 

 glands then secrete digestive ferments, absorb the products, 

 and then the leaf becomes unrolled again. 



The leaves of Sundew (Drosera) bear numerous stalked 

 glands or tentacles which secrete a sticky fluid (Fig. 65). If 

 an insect adheres to the tentacles, they bend down upon it 

 and pour out a fluid which has the 

 power of digesting, and rendering solu- 

 ble, albuminous or proteid substances 

 (white of egg, meat, etc.) in a similar 

 manner to that occurring in the stomach 

 of an animal. The secreted fluid is 

 reabsorbed, together with the soluble 

 nitrogenous products (peptones). When 

 digestion is completed, the tentacles 

 resume their former position, and are 

 then ready to capture another insect, 

 a process which may be repeated several 

 times. The tentacles may be stimulated 

 to movement by continued contact with 

 any solid substance, but apparently no 

 digestive fluid is secreted unless a suit- 

 able organic substance e.g. a piece of 

 meat or of boiled egg-albumen is placed on the 



Fig. 65. Leaf of Sundew. 



Tentacles expanded on the 

 right ; partially inflexed 

 over an insect on the 

 left. 



raw 

 leaf. 



The Bladderwort (Utricularia) is a submerged water- 

 plant which has no roots ; the submerged parts show no clear 

 division into leaves and branches, but are finely divided, and 



