222 The Botanical Gazette. [June, 
pulvinus. Fig. 11 shows the divisions of the fibrovascular 
parts as they enter the lamina of the leaf. At point vis 
shown a portion of a longitudinal section of one of the veins 
of the lamina. Fig. 12 is from a dorsiventral median longi- 
tudinal section of the upper pulvinus, point x being the lower 
and point y the upper end. In this section the fibrovascular 
portions appear only in a single line as they pass through the 
pulvinus. 
From an examination of the nine drawings just explained 
it is evident that the fibrovascular bundles, which in the petiole 
are arranged in asingle completed ring, are rearranged as they 
enter the pulvinus in -a plane corresponding with that of the 
lamina of the leaf, thus offering the least resistance to vertical 
movement. 
Francis Darwin‘ describes the first appearance of the pul- 
vinus in the cotyledons of seedlings of Oxalis corniculata as @_ 
transverse zone of longitudinally compressed parenchyma 
cells. This transverse zone of cells he says makes its ap- 
pearance about the second day of germination. In the plant 
under study it is possible to demonstrate leaves in the umop- 
ened winter buds of much less development than in the a 
cited by Darwin. By means of serial longitudinal sections © 
leaf buds passing dorsiventrally through the leaf petioles, 
leaves were found in which no evident trace of a pulvinus 
could be made out. This is true, however, only of the most 
minute traces of leaves; that is, leaves in which no differenti- 
ation into lamina and petiole could be made. In these yt 
bryonic leaves the first appearance of the pulvinus may in 
demonstrated. The pulvinus, as I believe, comprise 
the broadest sense simply a continuation of 
phyll tissue of the lamina down the petiole 0 
More carefully stated, it is an enlargement 
of the lamina of the leaf. It is a well known fac he la 
gradations of connection between the stipules*® — - ules 
mina of the leaf in various plants can be traced. The sully 
may be a part of the lamina, or they may be only Pe may 
separated from it leaving a winged petiole, or the pett©! 
- : ng + 
be naked as in the case of Cercis Canadensis leavll — 
“The Power of Movement in Plants 119. 1831. 
5Gray’s Botanical Text Book, sixth edition, 1: 105-107. 
