488 The Botanical Gazette. [December, 
cribed but have square end walls. They are of the same col- 
lenchyma type as shown in the organ of the petiole, but the 
thickening at the corners is not quite as marked. In Trifolium 
repens the walls of the pulvinus parenchyma cells are slightly 
thicker than the walls of the adjacent parenchyma. A few of 
the cells for that organ are shown in fig. 5; as compared with 
those, a few cells from the organ of Melilotus alba are shown 
in fig. 6. The difference in the thickness of the cell walls is to 
be noted. The cells are about equal in their tangential and 
radial dimensions but their length is slightly less. No inter- 
cellular spaces whatever could be detected, but the whole 
of the hypodermal cells are richly filled with chlorophyll 
bodies, while the protoplasm always occupies the periphery 
with a large vacuole in the center. 
In the diurnal position the organ is slightly curved and 
shows very marked and regular transverse wrinkles for the en- 
tire length. When the organ assumes its night position it 
becomes more curved; the wrinkles on the ventral side be- 
come more marked while those on the other side are to a Cer- 
tain extent obliterated, figs. 7and 8. These organs are con- 
tractions rather than enlargements of the petiolule. The 
same distortion of the cells in the region of the transverse 
depressions is to be noted as in the primary organ. 
The schizosteles,-as they emerge from the primary organ, 
traverse the petiole in the position shown in fig. 9 and give 
off lateral branches to the secondary motor organs in which 
they still occupy the center. The stele with its surrounding 
bast fibers is circular in cross section to agree with the form 
of the organ itself and it shows the same remnant of pith as 
in previous cases. By comparing the cross sections of the 
steles of the petiole and motor organs, it is found that the 
elements have been reduced in size; the bast fibers have 
thicker walls and are decidedly smaller, while the sieve cells 
have undergone such a modification in the thickness of their 
walls that it is almost impossible to tell which are bast fibers 
and which sieve cells, so closely do the two regions merge 
into each other. Otherwise the arrangement is very similar 
to that described for the primary organ, so no further des- 
cription is needed. In the rachis the schizosteles occupy the 
same position as in the petiole and at the end come together 
to form the central stele of the terminal leaflet. 
4 
