308 



Biology in America 



and some of its roots are left embedded in the ground. Soon 

 the young flexible branches turn and grow upward opposite 

 to the direction of gravity. Roots, on the contrary, when 

 placed in a horizontal position, or inverted so as to point 

 upward, will soon respond to the pull of gravity and grow 

 downward. A seedling is suspended with its rootlets im- 

 mersed in a stream of water, and soon they bend and grow 

 against the current of the stream. Touch the leaves of the 

 Mimosa or sensitive plant and almost immediately the paired 



MINOSA OR SENSITIVE PLANT 



From Kerner (translation by Oliver), "Natural History of Plants," 

 Henry Holt and Company. 



lobes of the leaflets fold together and the leaf itself droops 

 slightly, soon however resuming their original position if un- 

 disturbed. 



The flowers of some plants serve as insect traps. In the 

 sun dew (Drosera) the leaves are covered with numerous little 

 hairs or tentacles, which secrete a sticky fluid, which glistens 

 in the sun like drops of dew, whence the plant derives its 

 common name of "sun dew." Certain glands in the leaf 

 secrete a digestive enzyme similar to the pepsin of an animal 's 

 stomach. If a drop of rain, or a grain of dust blown by 



