1894. ] Leaf Movement in Cercis. 223 
stipules entirely distinct. With equal propriety a portion of 
the leaf lamina may remain in connection with the petiole and 
by special modification be changed into an organ for the pro- 
duction of motion. By means of dorsiventral longitudinal 
sections of the smallest leaves in which a distinction of parts 
could be made, the structure of the leaf, with the exception 
of a layer of epidermal cells along the dorsal (lower side when 
the leaf is expanded) surface together with a few parenchyma 
cells, was found to be uniform throughout. The next stage 
of development examined showed traces of scalariform ves- 
sels with evident parenchyma in both petiole and lamina. In 
the largest leaf which could be obtained from an unopened 
leaf-bud the parenchyma and fibrovascular portions of the 
petiole and lamina were found to be well developed and at a 
Point in the petiole near the base of the lamina were to be 
seen a number of parenchyma cells showing evident irregular 
cell division. This irregular cell division I consider as the first 
appearance of the pulvinus. It corresponds closely with that 
taking place in the increasing mesophyll tissue of the lamina of 
the leaf and is in fact connected withit. Examination of more 
advanced leaves shows only an increase in number of these ir- 
regular cells until the mature pulvinus is reached which is 
fomposed in the main of loose irregular parenchyma. In 
Contrasting the first appearance of the motile organ in the plant 
under study with that noted by Darwin in the case of Oxalis 
Serniculata, I should say that while he observes the first ap- 
pounce of the zone of cells which is to become the pulvinus 
rom the fact of ‘the transverse regularity of the cells, the 
act of the j 
ee regular cell division in the remaining portion of the peti- 
cart Summary it may be said that the pulvinus of Cercis 
ench "-* SOnsists in the matise form of collenchyma, par- 
With the bast and woody tissue so arranged as to produce 
Under th ©ast expenditure of energy on the part of the plant 
ina of eauiluence of light a daily movement in the leaf lam- 
to be nearly one hundred degrees. This motile organ is 
ittepyl waered as a development through multiplication by 
ivision of a portion of the parenchyma tissue at 
PPer end of the petiole, and moreover the development 
