UTRICULARIA: GENLISEA 



281 



remains of which Goebel found the bladders filled. These 



may enter through the passage formed by the terminal 



twisted branches, or directly through 



the slit which terminates the canal. In 



either case they cannot retreat, for the 



passages and canal are furnished with 



rings of hairs, all pointed towards the 



bladder. Whether the prey is digested 



or the plant merely absorbs the products 



of bacterial decay is not known : glands 



occur in the bladder. 



General Considerations. — The capture 

 of animals has been conclusively demon- 

 strated in all these insectivorous plants ; 

 in many cases, as we have seen, active 

 digestion occurs, F. Darwin (1880) 

 showed for Drosera that plants fed with 

 insects, or with egg albumen, or with 

 pieces of meat thrive better than those 

 deprived of a flesh diet. Biisgen raised 

 sundew plants from seed, and found 

 that those provided with an animal diet 

 produced more flowers, more and larger 

 capsules, and more numerous seeds than 

 controls. It is generally believed that 

 the chief advantage lies in an increase of 

 nitrogenous food supply. Stahl lays 

 stress on the addition of other salts. It 

 is likely that this, too, is important, for 

 the root systems are typically scanty, 

 but exact experiments on this point are 

 wanting. There is the further possibility pj^ 41. — Bladder 

 of an absorption of organic carbon com- ^J^^i^^^Afte^Goe- 

 pounds. But Kostychew (1923) has shown bel.) " 

 that, in an atmosphere rich in carbon 

 dioxide, Drosera and Pinguicula assimilate as vigorously as 

 plants Hke the coltsfoot. 



As to the origin of the habit not much can be said with 



