HISTORICAL REVIEW "J 



tlons were offered for practically all reactions and other 

 physiological phenomena In animals, and the same may be 

 said with regard to plants, as will be shown in the following 

 pages. 



Toward the close of the seventeenth century, the striking 

 movements of the sensitive plant, Mimosa, imported from 

 America, attracted considerable attention. Ray described 

 the movements of this plant In his " Historia Plantarum" 

 (1693), and although an apparent believer in the soul of 

 plants as defined by Aristotle, he tried to explain the move- 

 ments mechanically. He thought that they were due not 

 to sensations but to physical causes, — " Planta est corpus 

 vivens non sentlens." The leaves remain erect, he said, 

 because of the constant flow of sap Into them. When 

 touched, the tubes which carry the sap to them are par- 

 tially closed, and thus the supply of sap is diminished to 

 such an extent that the leaves are no longer held erect and 

 consequently droop. He was of the opinion, that plants 

 bend toward a window because of difference In rate of 

 growth on opposite sides due to difference In temperature. 

 It was known in a general way that an increase in tempera- 

 ture causes an Increase In the rate of growth In plants; 

 and Sharroc had found that the stem on which he was 

 experimenting grew toward that part of a window where 

 air entered through an opening. It was from these obser- 

 vations that Ray reached his conclusions. 



At about the same time Dodart came to the conclusion 

 that physical contraction of the fibers on the moister side 

 of roots and their expansion on the moister side of stems 

 caused the former to turn down and the latter up. 



Du Hamel, after studying the effect of light, temperature 

 and moisture on the direction of growth, concluded that 

 the " Richtung der Dampfe " in the vessels and around 

 the plant Is of prime Importance, and that if heat, light 

 and moisture have any influence on the direction, It Is 

 through their effect on the gases. Ridiculous explanations, 

 all of them, in the light of present knowledge! But, even 



