MOVEMENT IN PLANTS 



117 



creep through the soil. But the vast majority of plants, trees 

 and shrubs and flowering plants, and mosses and mushrooms 

 and seaweeds are rooted in the soil or to some base, and 

 their food flows round them: they have no need to go after 

 it, nor after the oxygen which they respire. But their im- 

 mobility has its dangers: they cannot move away from a 

 vitiated atmosphere, or from the neighbourhood of danger, 

 or from anything that bores them. 



Although few plants move as a whole and these almost 

 entirely water-plants, their parts move. We have seen above 

 that the protoplasm in the cells is in a constant state of 



1V-- Jl 



(2) ■• (S) •• " (4) 



Fig. 37. Stages in the collapse of a cell when immersed in a strong solution: 

 in (1) it is fully turgid, with the cell-walls distended; in (2) the cell- wall is 

 no longer stretched, and the cell is therefore flaccid but the protoplasm is still 

 in contact with the cell- wall; in (3) plasmolysis has begun, and in (4) the 

 protoplasm has rounded off and only remains in contact with a small part 

 of the wall, w, cell- wall; s, cell-sap, p, protoplasm; n, nucleus; c, chloroplast; 

 e, solution which has passed through the wall of the cell. After De Vries, 

 modified. 



movement. It circulates and flows hither and thitlier. But 

 although in all higher plants the whole organism does not 

 move — is not in fact locomotive — parts of the whole do move. 

 This they generally do by their tissues stretching and con- 

 tracting, and this is brought about by alterations in the amount 

 of fluid in the cells. Cells may he flaccid or turgid, limp or full 

 of water and stiff. Alternations in the turgidity of the neigh- 

 bouring cells produce movement. An actively growing stem 

 usually advances in an irregular spiral due to tlie growth ot 

 one side of the growing end being more rapid than the other. 

 Then again, the so-called telegraph-plant of India has leaves 



