70 PLANT PHYSIOLOGY 



wort (JJtricularia). These plants, which are either bog plants, 

 water plants, or epiphytes, contain chlorophyll but at the same 

 time are provided with a means for catching or holding small 

 animals, mostly insects, which are later digested. 



In the pitcher plants (Fig. 4A) all or a part of the blade is 

 modified into an urn or pitcher which fills with rain water, in 

 which any venturesome insect is drowned and subsequently di- 

 gested. Hairs pointing inward and downward prevent the escape 

 of the prey. 



The sundew (Fig. 4B), characteristic of peat bogs, has a leaf 

 blade covered with pin-shaped glandular hairs that secrete at 

 their tips a digestive enzyme. When an insect alights upon the 

 leaf, it is held fast as the hairs bend in toward it. At the same 

 time, the digestive enzyme continues to be secreted until all 

 utilizable portions have been absorbed, when the hairs open up to 

 their original position. The sundew is also able to digest lean 

 meat and egg white placed upon the leaf. 



In Dionsea (Fig. 4C) the end of the blade is divided by the 

 midrib into two hinged valves bearing long teeth along each 

 margin and three sensitive elastic bristles on the upper surface of 

 each half. When an insect alights upon the leaf and touches a 

 bristle, the two halves fold together very quickly thus imprisoning 

 the insect, which is later digested by an enzyme secreted from 

 glandular hairs on the leaf surface. 



JJtricularia (Fig. 4D) is a submerged rootless plant which 

 bears on the branches as modified leaves numerous hollow blad- 

 ders, which have only one entrance and that closed by a kind of 

 trapdoor opening only inward. Small water animals which are 

 drawn into the bladder through this entry are thus shut off 

 from escape. and are later presumably digested. Although Stutzer 

 (1926) thinks the digestion is brought about by bacteria in the 

 bladders, which probably take some of the food for themselves 

 and thus furnish another example of symbiosis, Adowa (1924) 

 found proteases present, which he thinks came from the JJtricularia 

 itself. 



Although the insectivorous plants are among the few which 

 are especially adapted for supplementing their food supply in 

 this fashion, there are other autotrophic plants which can use 

 organic food. It has even been suggested (Christy, 1923) that the 

 common teasel (Dipsacus) augments its food supply in a manner 



