138 MOVEMENTS OF CURVATURE 



of the pulvinus of Mimosa pudica increased in the evening, so that the sleep-move- 

 ments are not produced by one-half of the pulvinus becoming flaccid, as are those 

 following mechanical excitation. A natural result of this fact is that in the drooping 

 evening position the main pulvinus is still capable of a pronounced curvature in 

 response to mechanical excitation J . Long before Briicke's time Dutrochet 2 had 

 concluded, mainly from observations upon operated pulvini, that the sleep-movements 

 were due to opposite changes of the energy of expansion in the antagonistic halves of 

 the pulvinus. Dassen, Briicke, and Sachs 3 came into more or less accordance with 

 this view, whereas Millardet 4 and Bert 5 concluded that the changes of expansion 

 were alike in character in both halves, but differed quantitatively, and also in their 

 progress in time. The subject was then fully explained as in the text by Pfeffer's 

 researches. Previously to these researches the effects of the periodicity and of the 

 direct stimulation were not properly distinguished, with the result that the observa- 

 tions upon operated pulvini led to contradictory conclusions. The completeness of 

 the operation is also of great importance, for if the parenchyma is removed from the 

 upper half of a pulvinus of Phaseolus down to the upper surface of the vascular 

 cylinder only, a fall is produced by darkening just as in the intact pulvinus, owing to 

 the fact that the expansive energy of the remaining portion of the pulvinus is still 

 greater than that of the lower half. If, however, the parenchyma is removed down to 

 a plane passing through the middle of the vascular cylinder, the leaf rises in darkness, 

 showing that the expansive energy of the lower half of the pulvinus has increased 6 . 

 It was probably owing to the incomplete removal of the upper half of the pulvinar 

 tissue that Schwendener and Jost 7 obtained contrary results with Phaseolus, while 

 Schwendener observed in a few other cases a shortening of the remaining half of the 

 pulvinus on darkening, if this is the half which is compressed when intact. Panta- 

 nelli 8 has found recently that both halves of the operated pulvini of Robinta pseudacacia 

 and Porliera hygromelrica react similarly to darkening. Schwendener 9 also observed 

 that after operation the main pulvinus of Mimosa pudica carried out the same daily 

 movements as before, provided that the periodicity was not disturbed by any exces- 

 sive and abnormal photonastic reaction. This result confirms that obtained by 

 Pfeffer. 



1 Ewart, Annals of Botany, Vol. XI, 1898, p. 453. 



2 Dutrochet, Rech. anatom. et physiol. s. la structure inthne d. animaux et d. vege"taux, 1824, 

 p. 134. For the detailed literature see Pfeffer, Period. Bewegungen, 1875, pp. 6, 163 ; Physiol. 

 Unters., 1873, p. 3. Cf. also Schwendener (1896), Gesammelte Botanische Mittheilungen, Bd. n, 

 p. 219. 



8 Sachs, Bot. Ztg., 1857, No. 46 a, 47. 



* Millardet, Nouvelles recherches sur la pe'riodicite de la tension, 1869, PP- 3 1 * 4 8 - 



5 Bert, Me"m. de la Soc. d. scienc. physiques et naturelles de Bordeaux, 1870, p. 51 of the 

 reprint. Cf. Pfeffer, 1. c., 1875, p. 7. 



6 Giessler and Wiedersheim have repeatedly found that the completion of the removal of the 

 upper half of the pulvinus always results in the shortening of the lower half on darkening being 

 converted into a lengthening. These results therefore confirm the original ones by Pfeffer (1. c.). 



7 Schwendener (1898), Gesammelte Bot. Mittheilungen, Bd. II, p. 246 ; Jost, Jahrb. f. wiss. 

 Bot., 1898, Bd. xxxi, p. 370. 



8 Pantanelli, Studii d' anatomia e fisiologia sui pulvini motori, 1901, pp. 225, 230. 



9 Schwendener, 1897, 1. c., p. 229. 



