150 ON THE POWER OF MOVEMENT IN PLANTS. 



coming off like a cap, as in Pimpernel, or by genuine valves, or 

 uplifting flaps, is in all cases governed by the same physical forces, 

 where also the varying anatomical structure of the several layers 

 bears a part. Examples are seen in the twisting of the awns of 

 Oat and other grasses, in the separation of the fruit-valves of 

 Wallflower, Geranium, Spurge, and perhaps most notably in the 

 capsules of the Balsam^ Impatiens-Noli-me-tangere^ taking its name 

 from the fact that when ripe, you have only to gently press the 

 middle of the capsule, when it suddenly coils up from each end, 

 the middle part rises into a hump, and the seeds are shot out, as I 

 have seen them often, to a distance of six or seven yards. 



We will now pass on to the third and the most interesting 

 class, where we find ourselves surrounded by phenomena at once 

 wondrous, varied, and beautiful in their complexity and adaptation 

 to useful end and purpose. 



CLASS III. 



Movements occurring in Living Parts of Plants during 



Active Growth. 



We are confronted at the outset with an almost insuperable 

 difficulty, viz.^ the classification of such movements. After trying 

 three or four systems, I have selected the following as, on the 

 whole, best suited to my purpose in a paper such as this ; it is to 

 group them under two heads : Periodic — £^., occurring at regular 

 times and under constantly similar circumstances ; 2ind I?iduced-i.e., 

 brought about by, for the most part, mechanical stimuli, such, for 

 instance, as touch, concussion, etc., not simply by heat or light. 



Under both these divisions we come upon instances where 

 external influences are brought into play, and instances where, 

 seemingly, it is not so. The two divisions, however, merge into 

 each other almost insensibly, and many instances would fairly 

 come under both heads, as we shall see. Others are with difficulty 

 localised under either, as, for example, the constant movement all 

 through life of some roots and stems. I can only lay before you a 

 selection in each division, and only briefly touch on even these. 



A. — Periodic Movements. 

 The morphology both of this movement and the Induced 

 kind, consists for the most part of a folding up, or curvature of 



