268 Mr. D. D. Cunningham. On the Relation of [Nov. 16 r 



relative size. Not any of the above named fossils appear to me to call 

 for a Plate. 



III. " On the Relation of particular Structural Features in 

 certain Leaves to the Phenomena of Nyctitropism and 

 Movements incident on Stimulation by Concussion." By" 

 D. D. Cunningham. Communicated by Sir J. Hooker, 

 K.C.S.I., F.R.S. Received June 29, 1882. 



(Abstract.) 



The leaves forming the subjects of special study were those of the 

 following species : — Mimosa pudica, Neptunia oleracea, Pitliecolobium 

 Saman, Albizzia Lebbeh, Leucaena glauca, Cassia alata, and Cassia 

 sumatrana. In all of them nyctitropic movements occur, and in all,, 

 save those of Albizzia Lebbeh, in which the point has not yet been 

 determined, movements also follow stimulation by concussion. The 

 movements in individual instances, however, clhTer greatly in cha- 

 racter, in degree, and in persistence in relation to the life of the 

 leaves. The differences in regard to the rapidity and extent of move- 

 ment incident on concussion are specially marked. In Mimosa pudica 

 and Neptunia oleracea such movements are very extensive and rapid ; 

 in the two species of Cassia they are very slight and gradual, and 

 those in the leaves of Pithecolobium Saman and Leucaena glauca are 

 of an intermediate character. In some cases both classes of move- 

 ments persist from the period at which they first manifest themselves 

 until the death of the leaves, but in others they diminish with 

 increasing age, and disappear long ere death ensues. 



The paper is divided into three principal sections. The first of 

 these deals with the structural features of the individual leaves, the 

 second with the phenomena of movement, and the third contains a 

 comparison of the structural and motorial phenomena with a view to 

 determine how far these are essentially related to one another. 



In the first section it is shown that the contractile organs which are 

 the chief determinants of movement are, throughout the entire series 

 of leaves, specially characterised by the porous nature of their com- 

 ponent tissues. The porosity is very various in degree in different 

 cases, and, according to the extent to which it prevails, converts the 

 entire pulvinar organs, to a greater or less degree, into masses of a 

 spongy texture, specially fitted to allow of the ready redistribution 

 of fluid contents. In those cases where it is most highly developed, 

 as in Mimosa pudica and Neptunia oleracea, the pulvinar parenchyma is 

 composed in greater part of finely porous cells, and in some portions 

 contains masses of cells which, in addition to the fine pores, arc 



