164 BOTANICAL GAZETTE [MARCH 
The upper surface of the plant is divided into small areas as 
in Marchantia, and in the center of each of these areas Leitgeb 
discovered a simple air pore surrounded by about six guard cells 
(figs. 10, zr). Two or three tiers of air chambers compose 
the green tissue, the walls and roofs of the chamber being 
composed of chlorophyllose cells. The storage tissue, composed 
of about ten layers of colorless, starch-filled cells, forms a strip 
beneath each dorsal furrow. The method of growth of the 
eho 00. 
Ricciocarpus natans. 
Fic. 4.—Diagram of longitudinal section of 
ge aes dorsal furrow, showing the ventral plates, a group 
: of archegonia in different stages of development, 
and further back a group of antheridia. 
thallus and the formation of air chambers, air pores, and ventral 
scales has been so thoroughly worked out by Leitgeb (6) that 
there is little to add to his account. The number of apical cells 
at the anterior end of each furrow is larger than he supposed, 
averaging about five in our plants, as may be seen from the 
number of rudiments of ventral scales in a nearly horizontal sec- 
tion taken just below the apex (fig. g). The position of the 
apical cells and their relation to the ventral scales is made cleat 
by the sections represented in figs. 4, 7, 8, 9. 
The dorsal furrow in cross section has somewhat the form of 
an inverted Y, with a more or less prominent median longitudinal 
ridge between the arms. Early observers supposed this ridge ee 
