THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 57 



conspicuously in the circulation of sap. It might, indeed, be 

 concluded a priori, that through plants displaying much 

 differentiation of parts, an internal movement must be going 

 on; since, without it, the mutual dependence of organs 

 having unlike functions would be impossible. Besides 



keeping up these motions of liquids internally, plants, espe 

 cially of the lower orders, move their external parts in rela 

 tion to each other, and also move about from place to place. 

 There are countless such illustrations as the active locomo 

 tion of the zoospores of many Algce, the rhythmical bondings 

 of the Oscillatorice, the rambling progression of the Diato- 

 macecB. In fact many of these smallest vegetals, and many 

 of the larger ones in their early stages, display a mechanical 

 activity not distinguishable from that of the simplest animals. 

 Among well-organized plants, which are never locomotive in 

 their adult states, we still not unfrequently meet with rela 

 tive motions of parts. To such familiar cases as those of the 

 Sensitive plant and the Venus fly-trap, many others may be 

 added. When its base is irritated the stamen of the Ber 

 berry flower leans over and touches the pistil. If the 

 stamens of the wild Cistus be gently brushed with the finger, 

 they spread themselves: bending away from the seed-vessel. 

 And some of the orchid-flowers, as Mr. Darwin has shown, 

 shoot out masses of pollen on to the entering bee, when its 

 trunk is thrust down in search of honey. 



Though the power of moving is not, as we see, a character 

 istic of animals alone, yet in them, considered as a class, it is 

 manifested to an extent so marked as practically to become 

 their most distinctive trait. For it is by their immensely 

 greater ability to generate mechanical motion, that animals 

 are enabled to perform those actions which constitute their 

 visible lives; and it is by their immensely greater ability to 

 generate mechanical motion, that the higher orders of animals 

 are most obviously distinguished from the lower orders. 

 Though, on remembering the seemingly active movements of 

 infusoria, some will perhaps question this last-named con- 



