356 PHYTOLOGY. 



Of Motion in Vegetables. — All plants are not endowed with, evident 

 motion, many being perfectly at rest, having no actions going on in 

 them but those of simple growth, which is the most simple state in 

 which we can conceive life to exist. 



Some, however, have motions produced in parts of them, from par- 

 ticular causes, as the rising or setting of the sun, &c. Others are 

 affected by the touch, so as to be immediately put into motion. Some 

 have diurnal motions going on regularly and uninterruptedly, but so 

 exceedingly slow, as to be with difficulty perceived: others, again, 

 have constant motions, at least through the day, going on so quickly as 

 to be easily detected by the eye 1 . 



On what circumstances these motions immediately depend, — whether 

 they arise from the action of structures formed for this purpose, or from 

 a series of contiguous structures so conjoined as to produce the effect 

 by their successive motions — we are at present ignorant. It is probable, 

 however, that the power is analogous to the irritability of animals. 



Some vegetables have their leaves closed up in the evening, as the 

 Sensitive-plant ; in .most they are not in the least affected by either 

 evening or day. 



To ascertain the cause of the internal influence which produced 

 these effects in the first, I made several experiments. As the visible 

 difference between day and night are heat and cold, light and darkness, 

 I made the following experiments upon these principles : — 



For distinction, I shall call that action which appears to arise from 

 the greatest quantity of vigour, extension; and that action which appears 

 to arise from a loss of power, flexion ; although many of the motions 

 themselves, with regard to the position of parts, are not always 

 strictly so. 



I took a Sensitive-plant, and in the evening, when it was in a state of 

 flexion, put it into a room. At five o'clock in the morning, a little 

 while after sunrise, it was beginning to expand its leaves and erect its 

 stalks, and continued this position till about five o'clock in the evening, 

 when it began to close again, but before the light was materially gone. 



The second day I kept the room dark till five o'clock in the after- 

 noon (the time that the others were beginning to close), and it ex- 

 panded itself and kept expanded till dark, when all its extremities 

 began to collapse. 



of plants are very imperfectly known. "We have little acquaintance with the plants 

 of hot countries ; and those of Europe hare been more studied for their uses than 

 for the advancing of natural knowledge."] 



1 [In the Hedysarum gyrans (Desmodium, Decandolle) there is a continual motion 

 of the leaves by day, independently of atmospheric movements.] 



