1882.] Structural Features to Nyctitropism, fyc. 26 ( J 



provided with one or more large ostiola — rounded openings with, 

 thickened margins. Here, also, an enormously developed system of 

 very large intercellular spaces is present in the deeper layers, commu- 

 nicating freely on one hand with the cavities of the porous cells and 

 on the other with a system of channels traversing the epidermal 

 tissues of the petiolar organs. In less developed cases, such as those 

 of t^e other species treated of, pores alone are present in the cells, 

 ostiola are entirely absent, and the system of intercellular spaces is 

 feebly represented or almost entirely suppressed. The vascular 

 bundles are in all cases characterised by an abundance of porous 

 elements, both in the bast and very especially in the wood, where a 

 svstem of large porous ducts almost entirely replaces the spirals of 

 the axial and petiolar tissues. 



Another very important structural feature in the contractile organs 

 is the existence of very marked inequalities in the strength of the 

 formed elements of the tissues of different areas, as well as local 

 variations in the amount of protoplasm and specially of chlorophyll 

 corpuscles in different portions of the superficial parenchyma. 



In the second section of the paper special attention is drawn to the 

 fact that the maximum nocturnal position appears in all cases to be 

 normally attained at a relatively early period after the onset of dark- 

 ness, and that, after this, a reverse movement, tending more or less to 

 the resumption of the diurnal position, sets in independent of any 

 renewed incidence of light. In connexion with this it must be noted 

 that the movements incident on concussion by stimulation tend 

 towards the assumption of the initial nocturnal position. 



The third section of the paper contains an attempt to demonstrate 

 the existence of an essential connexion between the special structural 

 and motorial phenomena in individual leaves. It is pointed out that 

 the occurrence of movement incident on stimulation by concussion is in 

 all these cases associated with the existence of structural arrange- 

 ments in the contractile organs specially calculated to facilitate redis- 

 tribution of fluids in the tissues, and that the rapidity and magnitude 

 of the movements in individual cases bear a direct relation to the 

 degree of development of such structural features. For example, in 

 Mimosa puclica we find very rapid and extensive movements associated 

 with extreme porosity of the cells of the pulvinar parenchyma, and 

 with the presence of a very highly elaborated system of intercellular 

 spaces. In other cases, such as that of Pithecolobium Saman, we have 

 more limited and gradual movement along with less elaboration of 

 porosity and diminution of the intercellular system, and in the case of 

 the two species of Cassia we encounter minimum development of the 

 special structural features with minimum development of concussion 

 movements. This appears to indicate that rapidity and extent of 

 concussion movement may be ascribed rather to structural than func- 



