20 MOUNTAIN AND MOORLAND 



free movement. One does not, perhaps, expect them 

 to prowl about; but one knows how Sundews move 

 their tentacles and Fly-Traps their leaf-blades, how the 

 leaflets and leaves of the Sensitive Plant move when 

 one touches them, how the tips of seedlings bend and 

 bow in a leisurely way to the different points of the 

 compass, how roots in an earthworm's burrow move 

 like shoots, how tendrils coil round their support, 

 and one asks again, why plants should move so 

 little. 



The day is young yet, and this is a pleasant bank, so 

 we may give the three answers that we know, (i) 

 First, there is a great deal more movement about the 

 young and growing parts of plants than most people 

 think. (2) In the second place, except as regards car- 

 bonic acid gas, plants are not able to get rid of their 

 waste products as animals do, and we feel sure that 

 this must mean a serious handicapping of activity. 

 Plants are like smouldering fires, in some danger of 

 being smothered in their own ashes. (3) But, thirdly, 

 the living unit or cell of the plant is shut up in a pro- 

 tective wall of cellulose, which seriously hinders 

 mobility. It is a fact, we believe, that almost all the 

 movements of parts of plants are due to change in the 

 turgor or water-pressure of the cells. As Professor 

 F. O. Bower has said in his fine " Botany of the Living 

 Plant" (1919), "Like the mediaeval knight, the move- 

 ments of the plant protoplast are checked by its pro- 

 tective armour. The plant has sacrificed mobility fof 

 mechanical defence." But it is very useful for us to 

 look at movements like those of the Sensitive Plant, 

 the Fly-Trap, the coiling tendrils of the Pea, and the 

 Rock Rose's stamens, to feel that there is a good deal 



