158 BOTANICAL GAZETTE [MARCH 
The chlorenchyma is differentiated into a typical and very com- 
pact palisade tissue of two strata, and a pneumatic tissue of oblong 
cells (in transverse section) more or less vertical to the blade and 
with very wide intercellular spaces. The mechanical tissue occurs 
only as collenchyma, which follows the veins and which is best 
developed on the leptome side. A small isolated mass of this 
tissue is also found in the margins of the leaf-blade. The collen- 
chyma is quite thick-walled and is located directly inside the epider- 
mis, but only as isolated masses above and below the nerves, besides 
in the margins. A thin-walled, colorless tissue, which evidently 
represents a water-storage tissue, is amply developed in the midrib 
and the larger secondaries, where it surrounds the mestome com- 
pletely. Crystalline sand was observed in some of the cells of this 
tissue. 
The mestome strands are all collateral, but the arrangement of 
the mestome is somewhat different. The smallest veins show an 
orbicular outline in transverse sections, and they are surrounded by 
a very distinct parenchyma sheath; in these the hadrome is located 
exactly above the leptome. On the other hand, in the midrib or the 
secondaries the mestome is in the shape of an arch with the ends 
curved inward, whose concave face looks toward the upper face 
of the leaf. In this arch the leptome follows the lower face and takes 
part in the curvature of the end; thus actually the leptome becomes 
moved from the lower to the upper portion of the mestome bundle. 
The hadrome is represented by numerous but short rows of vessels 
arranged above the leptome in the middle of the arch, but beneath it 
at the ends. 
The petiole.—The structure is exactly the same as that of the 
midrib in the blade. The single, very broad, and arch-shaped 
mestome strand is located in a mass of colorless parenchyma with 
crystalline sand, and possesses a support of well-developed collen- 
chyma, while chlorenchyma is completely absent. 
The characteristics of Cephalanthus, therefore, are the location of 
the phellogen inside the exodermis of the root; the absence of stereome 
in the leaf; the differentiation of the cortex of the stem into two dis- 
tinct cones interspersed with stereome; and finally the structure of 
the larger veins in the leaf with the arch-shaped mestome strand. 
