84 MISSOURI BOTANICAL GARDEN. 
really belong to the pulvinus of the leaf, but this does not 
prevent them from appearing as distinct cortical bundles in 
favorably located sections (pl. 39 and 44f.1-3). Three of 
these foliar bundles, corresponding to the three bundle 
traces evident on the scars marking the former position of 
fallen leaves, pass into each petiole, where they soon unite 
to form a closed crescent-shaped ring of bundles. No 
isolated bundles are contained within this petiolar ring, the 
parenchyma within which includes a series of about twenty 
secretion passages similar in structure and contents to those 
of the stem, with which, however, they have no direct com- 
munication. From the petiole, a group of resin passages 
runs through the midrib of the leaf, a single one passing out 
into each of the finer veins. Stellate crystals are of rather 
frequent occurrence through the petiole and midrib, both 
of which contain collenchyma. 
The upper epidermis of the leaf blade is smooth walled 
except for a few striated cells about the bases of some of 
the hairs, and consists of a layer of inconsiderably thick- 
ened cells, beneath which lies a layer of quadrate cells each 
of which contains a large stellate crystal. A layer of 
similar cells is also found between the veins and the lower 
epidermis, the cells of which are somewhat smaller and 
prominently wrinkled on the outer wall, so as to appear 
almost muricate in cross section. The stomata are not 
sunken below the general level of the epidermis. Tannin 
appears to be abundant in the epidermal layers. 
Pubescence consists of two kinds of hairs:— abundant, 
slender pointed thick walled hairs, usually with several 
transverse septa, especially toward the often bulbously 
widened base, and mostly isolated, but occasionally binate ; 
and.less numerous clavate hairs, septate both longitudinally 
and transversely, their small cells with yellow contents. 
These compound hairs are chiefly seen on the young stem, 
the sides of the petiole, and the upper surface of the mid- 
rib of the leaf. The epidermal cells about the bases of the 
hairs are usually divided by a septum parallel to the leaf 
20 
