56 THE AMERICAN BOTANIST 



of all, would be quite impossible. In fact there are some 

 movements peculiar to certain plants and dependent on tem- 

 porary or occasional factors which 'oecome modified by envi- 

 ronment. Every animal movement is the result of a tension 

 of muscles regardless of the stimulus; but such cannot be said 

 of plants. 



CIRCUMNUTATIQN 



The most common and universal movement found in the 

 plant kingdom is circumnutation. It is the elliptical or circu- 

 lar movement, made by apparently rvery growing ^art of all 

 plants. The movements vary greatly in form and amplitude 

 with different species. Some plants describe larger circles 

 than others, while those which describe ellipses have a still 

 greater variation. 



Circumnutation is brought about by a growth, first on one 

 side of the organ and then on the other. The cells become 

 steadily more and more turgescent on one side until the part 

 suddenly yields and bends. Then they become more so on the 

 other and the part swings around again. It is probable that 

 the more rapid the growth the greater the movement, until the 

 plant is full grown, at which time circumnutation would be 

 verv slight. Just why every part of a plant while it is grow- 

 ing and in some cases after growth has ceased, should have the 

 cells rendered more turgescent, and the walls more extensile, 

 first on one side and then on another, thus inducing circum- 

 nutation, has not been conclusively shown. But by all ap- 

 pearances it would indicate that the changes in the cells require 

 periods of rest. 



The seat of circumnutation in leaves generally lies in the 

 petiole, but sometimes in both the petiole and the blade or in 

 the latter alone. The extent of the movement varies in dif- 

 ferent plants. It is chiefly in a vertical plane,rising from 2 to 



