486 The Botanical Gazette. [December, 
equal dimensions radially and tangentially, but are shorter in 
the longitudinal direction in accordance with the general type 
of motor organ cells. In consequence of the thickening of 
the walls the cell cavities are more or less spherical, fig. 3. 
The epidermal cells of the dorsal side are larger than those 
on the ventral side. The internal walls are much thicker in 
the longitudinal direction than the external walls, and very 
much thicker than the radial walls (fig. 3). The ex- 
ternal wall also shows longitudinal ridges as in Trifolium pra- 
tense and other species. 
The cells of the hypodermal tissue are different upon the 
upper and under sides of the organ. Those immediately be- 
neath the epidermis are of about the same size as the epi- 
dermal cells, but towards the center the first few cells increase 
in size, then there is a decrease until the central stele is 
reached where they are even smaller than the epidermal cells. 
The cells of the dorsal side of the motor organ in the region 
of the hilum are smaller than tho$e of the other side and 
their walls are more uniformally thickened while the cell cavi- 
ties are generally four sided incross section. The remainder 
of the hypodermal cells are of the collenchyma type, fig 3. 
They are very much thickened at the corners and the middle 
lamellz are very marked. . The side walls, although they 
look thin when compared with the thickened corners, are yet 
very much thicker than the walls of the adjacent parenchyma. 
Upon the ventral side of the organ in the region of the depres- 
sion, which remains permanent, the cell walls are very thick 
and the cells irregular in shape. In some cases the opposite 
walls nearly touch each other, and when the nocturnal post- 
tion is assumed the cells in the region of all the transverse de- 
pressions become very much distorted in shape. In the region 
of the central stele there are a few intercellular spaces, but to- 
wards the periphery they are entirely absent. The cells near 
the axis cylinder contain an abundance of chlorophyll, but 
those near the surface have a less abundant supply. Like all 
those previously described the cells have a peripheral layer of 
protoplasm, with the center occupied by a large vacuole. a 
Cross sections of the hypopodium were cut, and the origin 
of the bundles from the axis which was externally indicated, 
was confirmed. The purely mechanical advantage of t : 
arrangement is at once clearly seen, and when itis noted me 
these three schizosteles come together at the base of the pul 
