2 BOTANICAL GAZETTE [JULY 
Sections of the structures studied were cut in paraffine, stained 
rather lightly in Mayer’s haemalum, and then strongly with 
Bismarck brown in saturated solution in 70 per cent. alcohol. 
THE LEAF. 
The leaves of Pilularia arise, in acropetal succession, on the 
right and left sides alternately of the upper surface of the stem. 
Each leaf originates in a large cell from which a typical two- 
sided apical cell is cut out by curved anticlines. The apical 
cell thus formed has its longer axis directed toward the stem 
apex (ZL, fig. 7), as was shown by Bower (84). 
This apical cell swells out beyond the general surface o 
the stem and cuts off segments, alternately toward the right 
and left of the latter and of the leaf itself. The number of 
segments formed is probably about fifteen pairs. In several 
young leaves where the segments could be counted the number | 
was found to be ten or eleven on each side of the apical cell, but 
in older leaves where the segments could not be satisfactorily — 
counted the number was apparently considerably greater, at 
least as many as fifteen. x 
By the growth and division of these segments a papilla-like 
organ is formed, which soon begins to curve in ventrally (Z, 
Jig. 3) toward and above the stem apex. This circinate coiling 
continues with growth of the leaf until, when a centimeter long, 
the tip may form a flat spiral of two turns or more, of which the 
inner projects out laterally beyond the plane of the outer, so 
that median sagittal sections cannot be obtained through the 
whole length of the leaf. 
Up to quite a late period the apical cell can be distinguished, 
but whether its fate is finally like that to be described for the — 
apical cell of the sporocarp was not determined. The shape of 
this is never three-sided, as described by Campbell (’93) in P. 
Americana, but is two-sided as stated by Meunier (’87), though 
the segments are not cut off toward the dorsal and ventral sides _ 
of the leaf as seems to be indicated in Meunier’s figures, but to 
the right and left alternately as we have seen. 
