358 A TEXT-BOOK OF BOTANY. 



to stimuli of different kinds, and are said to possess the property 

 of irritability. Movements of organs are of two general classes: 

 (i) Those due to stimuli which originate in the plant and (2) 

 those due to the influence of external factors. To the former class 



FlG. 205. Limnophila heterophylla, a marsh-plant belonging to the Scrophulariaceae 

 and growing in tropical Asia. The submerged or water leaves, below, are much divided and 

 arranged in apparent whorls; while the leaves at the end of the shoot above water are entire 

 and arranged in decussate dimerous whorls. In between occur transition forms, which are 

 divided and variously lobed and arranged in decussate whorls. After Goebel. 



belong all those movements which occur during the course of 

 development from the young to the mature stage. These are 

 known as growth movements or NUTATION. They are especially 

 noticeable in tips of growing branches, which instead of growing 



