LKSSO.N 27.] CIItCl'KATIOX IX C'KLI.S. 167 



(act with tlie earth and air on wliich tlicy feed, — the hit'.er and the 

 most important of these evci ywln re in>t tlie f«ame, — have no need 

 of locomotion, and so are generally fixed Aist to the spot where 

 they grow. 



481. Yet many plants move tlieir parts freely, sometimes when 

 there is no occasion lur it that we can understand, and sometimes 

 accomplishing by it sonn; useful end. The sudden closing of the 

 leaflets of the Sensitive Plant, and the dropping of its leafstalk, 

 when jarred, also the sudden starting forwards of the stamens of the 

 1 Barberry at the touch, are familiar examples. Such cases seem at 

 first view so strange, and so diflerent from what we expect of a plant, 

 that those plants are generally imagined to be endowed Avith a pe- 

 culiar faculty, denied to common vegetables. But a closer exam- 

 ination will show that i)lants generally share in this faculty ; that 

 similar movements maybe detected in them all, only — like those 

 of the hands of a clock, or of the shadow of a sun-dial — they are- 

 too slow for the motion to be directly seen. 



4S2. It is perfectly evident, also, that growtli requires motion ; 

 that there is always an intei-nal activity in living plants as well ;ls 

 in animals, — a power exerted which causes tli(;ir fluids to move or 

 circulate, and carries materials from one part to another. Some 

 movements arc mechanical ; but even these are generally directed 

 or controlled by the plant. Others must be as truly self-caused as 

 those of animals are. Let us glance at some of the priucijial sorts, 

 and see what light they tlirow upon vegetable life. 



483. CircillaliOll in Cells. From what we know of the anatomy of 

 plants, it is clear tiiat they have no general circulation (like that of 

 all animals cxcej)t the lowest), through a system of vessels opening 

 into each other (4(»2, 410). But in plants each living cell carries 

 on a circulation of its ouii, at least when young and active. This 

 may be beautifully seen in the transparent stems of Chara and many 

 other water-plants, and in tlui leaves of the Fresh-water Tape-Gniss 

 (Vallisueria), under a good microscope. Here the sap circulates, 

 often (juile liri>kly in appearance, (but the motion is magnified as 

 well as the olijects,) in a steady stream, just IxMieath the wall, 

 around each cell, pa-sing up (ine side, acro-s the end. down the 

 other, and so round to complete the cii-ciiit, carrying with it small 

 particles, or the larger green grains, which make the current inon^ 

 visible. This circulation may also be observed in hairs, particularly 

 those on flowers, such as the jointed liai''S of Spiderworf, looking 



