if TOR 



95 



g in plants growing under circumstances permitting of indefinite root 



differ 



and implying exposure to all possible variations in degree of atmospheric bumidit; 



Moreover, it is as a rule only in the tropica that phenomena of foliar movement occur 



with sufficient frequency, and on a sufficiently largo scale, to afford satisfactory 



pportunities for the comparative study of the peculiarities of movi merit in many 



mt species ; and it is only by means of such comparison that it is ]K)CBil>le to 

 determine how far any phenomena occurring in individual cases are really of peculiar 

 and specific nature. 



The movements which are executed by the leaves of Mimosa pudica are exceptional 



and peculiar as compared with any occurring among nyctitropic leaves in tenipcrat. 

 regions; but in any region in which Neptunia oleraeea occurs, or in which 

 nyctitropic leaves generally abound, it very soon becomes evident that the peculiarity is 

 one of degree and not of kind. The movements under certain circumstance! en 

 performed with exceptional rapidity, and in connection with the incidence of many slight 

 disturbing influences; but in the leaves of Neptunia tr>y may also occur with con idcrable 

 readiness and rapidity, and in many other common nyctitropic haves we find example! 

 of movements arising under circumstances similar to those under which the movements 

 of Mimosa and Neptunia manifest themselves. The nro\ merits certainly are neither so 

 readily evoked nor so rapidly executed as those of Mimosa and N/'/itma, but the differences 

 in this respect which are present among individual species of Common nyctitropic leave! 

 are almost as great as those existing between the movements of certain of them and those 

 of Neptunia, and certainly quite as great as those existing between the movement! of 

 Neptunia and those of Mimosa. Under favourable circumstances, a single light concussion 

 of a distal pinna may be sufficient to induce complete and very rapid action in a 

 leaf of Mimosa pudica; under similar circumstances, slow and limited action of a certain 

 number of pinnules, and possibly a certain amount of convergent movement in the pinna 

 subject to concussion, may occur in the leaves of Neptunia oleraeea: in PiM. olobium 

 saman a single concussion fails to produce any appreciable effect, but movements arise 

 under the influence of a certain number of repeated concu ions, the pinnules 

 gradually rise, the secondary rachises gradually converge and become depr< «1, and 

 the primary petiole converges where the primary pulvinus retains its activity; finally, in 

 Cassia alata very repeated agitation is necessary in order to secure the occurrence of any 

 appreciable movement in the pinnae. 



Phenomena demonstrating that particular agencies which induce movements in the 

 leaves of Mimosa pudica produce a like effect at a different rate in the leaves of other 

 nyctitropic leaves are constantly occurring. Separation from the axis under certain circum- 

 stances induces rapid and maximal movement in the leaves of Mimosa pudica and slow 

 and gradual movements in the case of other nyctitropic leaves, the displacement, whether 

 rapid or retarded, tending invariably to the establishment of the nocturnal position. The 

 impact of a single heavy drop of rain is in many cases sufficient to induce maximal 

 movements in the leaves of Mimosa pudica ; a brief exposure to a heavy shower sends the 

 leaves of Pithecolobium saman into the nocturnal position ; and prolonged exposure to violent 

 rainfall causes appreciable movements in the pinnae of Cassia alata. A single light breath 

 of air may be sufficient to cause maximal movement in Mnnosa pudica; repeated agitation 

 by a breeze cairses the leaves of Pithecolobium saman to move towards the nocturnal position; 

 and strong wind produces a like effect in the leaves of Cassia alato. Under exposure to 





