144 ON THE POWER OF MOVEMENT IN PLANTS. 



involving change of locality, or not involving it; whether it be 

 movement of a single cell, or a tissue of cells forming a plant, or 

 even of only the contents of a cell. 



It is quite impossible in a paper such as this to do more than 

 outline the subject, and by so doing, to try to give some notion 

 of the variety of movements to be met with, and, in some cases, 

 to point to examples. My paper will therefore be, in the strictest 

 sense, only an elementary chapter, written as it were with the 

 presumption that my readers know absolutely nothing of the 

 question, and that I am asked to try to tell them some simple 

 facts, to lead them just over the threshold of our inquiry, and 

 leave them there to pursue it for themselves. 



I do not intend to speak of passive movement at all : I mean 

 movement occurring as the result of external forces, such as wind, 

 or wave, or the weight of fruit ; nor of the means by which a 

 bough denuded of its fruit-weight goes back to the position it 

 occupied when that fruit existed only potentially in the blossom. 

 All I say will have direct reference to motion as the result of life and 

 its processes^ admitting only the mention of such external forces as 

 light and heat, to which an organism responds on virtue of the life 

 which it possesses. It will be seen instantly that such response 

 is active, and totally different from the passive movement above 

 referred to, which would ensue in inanimate bodies just as much 

 as in those endowed with life. 



There are several varieties of movement of which we might 

 speak, but we will confine ourselves to the chief of these, and where 

 it is possible to do so, find out how the motion comes about and 

 the use of such motion to the organism. 



I 



CLASS I. 



Movements dependent upon the Protoplasm contained in 



Plant-cells, or upon the presence of Cilia, or small 



Hair-like Processes on their surfaces. 



A. — Motion of the Contents of Cells. 



This is seen to be of two kinds : 



l.-Rotation^ where the current courses only along the walls either 

 spirally or reticulately. Remember, this is not, as it was formerly 



