226 



and in the course of a few hours it has moved downward through one 

 hundred and sixty or seventy degrees and the flowers are completely 

 immersed in water, where the development of the seed occurs. (See 

 Fig. 9.) 



The foregoing examples illustrate some of the principal or rather the 

 more apparent forms of movement, and the time is lacking to enumer- 

 ate others although of great importance and wide occurrence. It will be 

 more profitable to spend the remaining time at our disposal in a dis- 

 cussion of the movements. 



The external similarity of the movements of some plants to those of 

 animals has led to many ungrounded comparisons, and to the ascription 

 of sense or intelligence to plants. The questions at once arise in the 

 mind of a person who observes the movements for the first time : Have 

 plants muscles, sense-organs, and nerves, and is it conscious of the 

 movements ? 



In general I may snswer all of these questions by saying that the 

 mechanism of movement of plants offers only a general analogy to that 

 of animals, and that all motions are of a reflex character : The plant has 

 no nervous centre, but when a stimulus acts upon any part of the plant 

 the impulse is conveyed directly to the part of the plant producing the 

 movement. 



The plant has no structures which may be properly designated as 

 sense organs, yet there are certain portions which alone may receive 

 stimuli, and convert them into impulses The extreme tip of a root, 

 the blade of a leaf, the lower side of the tendril of the Passion Flower 

 are specially capable of sensibility. The Shameweed is however " sen- 

 sitive" over its entire surface with the exception of the flowers, seed 

 pods and upper side of the pulvinus. 



But movement is not produced at the extreme tip of a root or in ihe 

 blade of the leaf, or in other words the cells which receive the stimulus, 

 do not set up moi ion. The motile cells are at the base of the leaf stalk, 

 or at some distance from the " sensitive" cells. It will be convenient 

 to speak of the cells receiving the stimuli as constituting the " sensory" 

 zone, and the cells producing the movement as the " motor" zone. 



Now since the sensoiy and motorzones are separated by some distance 

 it is evident that tbere must be some sort of transmission of force from 

 one to the other. 'I he path along which the transmission is made has 

 not yet been made ont, that is to say the p ant has no known structures 

 analogous to the nerves of an animal. 



Although the mechanism by which movement is produced in plants is 

 not so well differentiated as that of animals, yet the degree of sensitive- 

 ness is in some instances even greater. 



Thus a tendril will curve in response to a weight not appreciable to 

 human touch and the shoot of a young plant will bend toward a light 

 which can not be perceived by the human eye. It is of interest in this 

 connection to note that many reputable biologists asci'ibe some form of 

 consciousness to plants ; the way is not clear to concur in this opinion 

 in the present state of our information on the subject. To recapitulate 

 the principal points in the foregoing discussion : 



The power of movement is quite widely distributed among plants and 

 is one of the most important means by which it adapts itself to its en- 

 vironment. The mode of life of the plant has tended to the loss of the 



