MOVEMENTS OF THE TARTS OF PLANTS. 553 



respect to this plant proves to us very clearly that, with regard to the 

 palpable parts of the phenomena, we have only obtained a mere sensa- 

 tionary knowledge of the rudest external aspect of the mechanism of 

 these motions, and that elaborate, careful researches must precede our 

 arriving at the point when the question of the cause of this phenomenon 

 can be put, and an explanatory theory of the movement can be proposed. 

 Until that time arrives, the reflective naturalist had better not enter into 

 any examination of hypotheses, or criticisms upon the explanations of 

 others. The uselessness of such a proceeding is evident. It would be 

 time wasted, time which might be much better devoted to the investi- 

 gation itself. 



Meyen, as has already been observed, has taken immense pains to arrive 

 at a conclusion, and in which, by means of some break-neck leaps by 

 way of inferences, he actually seems to have succeeded. Some experi- 

 ments, however (the only ones which I once had an opportunity of in- 

 stituting with a Mimosa pudica\ proved to me how little has as yet 

 been truly ascertained on this point, since they furnished me with re- 

 sults almost directly contrary to the statements of Meyen. The matter 

 stands thus : Meyen experimentalised on some very susceptible plants, 

 kept at a high temperature, being of opinion that this is the only way of 

 arriving at correct results. But this is opposed to correct practice, as the 

 least susceptible and strongest organisms are always selected for experi- 

 ments, by way of preference, in order to avoid unintentional secondary 

 interferences with the result of the experiment. A Mimosa, which is so 

 susceptible that it closes all its leaves upon the least shaking of the 

 ground, is certainly not well calculated for the purpose of showing that 

 it only closes some particular leaves on the division of its vascular bun- 

 dles. I purposely caused my plant, therefore, to vegetate for some time 

 at a low temperature, so that it did not close its leaves on slight shakings; 

 and the result was, that I found almost every thing different from what 

 Meyen had stated. It appeared to me that the loss of sap beneath a leaf 

 was invariably followed by a depression of the leaf, which continued 

 until the wound was closed by the coagulation of the sap. It is not, 

 however, worth while to communicate the details of these isolated obser- 

 vations,Jsince, so long as we are ignorant of the mechanism of the motion 

 itself, they could only give rise to useless guessing respecting the cause. 

 I can only assert again, that, hitherto, we are not only unacquainted with 

 the cause, but perfectly unacquainted even with the specialities of the 

 fact itself; and the same may be said of the movements of the other 

 plants mentioned. 



B. Movements independent of external influences. 

 a. Periodical. 



These are seen in some tropical species of Hedysarum, especially 

 H. gyrans L. and H. gyroid.es Roxb. The movements of the first 

 plant are known best of all, and are double. The compound leaf in 

 these plants consists of a couple of small lateral leaflets, and of a 

 large terminal leaf. The latter and the common petiole move up 

 and down according to the varying intensity of the light ; and the 

 terminal leaf is, especially in its changes of position, a most de- 

 licate photometer. These movements evidently correspond with 

 those enumerated under A., a. The two lateral leaflets, ho\vever, 

 exhibit a constant vibrating movement, every leaflet describing a 



