108 MISSOURI BOTANICAL GARDEN. 
angle is seldom less than 60° or greater than 90°, making 
the pouch shallow as compared with the foregoing species. 
The budding takes place from a slightly elongated placenta 
or matrix situated on the upper surface of the lower wall 
of the pouch, and the young buds are produced in regular 
order from near the pouch angle (pl. 66, f. 2-6). 
In developing, the young frond does not retain the same 
line of direction in growth as the parent assumes —the 
long axis of each crossing at an angle ranging between 
160° and 175°. In all the specimens examined, looking at 
the upper surface in each case, the young frond was turned 
to the right, away from the stipe scar of the parent, 
which is, in every case, on the left-hand side and under 
the young frond. The proportional distance of this 
scar from the two marginal angles of the pocket 
varies slightly, but in no case did I find it so near 
the left-hand angle as to warrant the drawings of Hegel- 
maier* which show it at the left-hand juncture of the upper 
and lower walls. He also figures the rows of elongated cells 
which form the costa as being situated in this line of junc- 
ture and extending from the scar to the basal angle of the 
pocket. My observations have shown the costa to be situ- 
ated within the lower wall of the pouch, about one-fourth 
the width of the pouch from the left-hand angle formed by 
the juncture of the two walls and never coinciding or 
parallel with it. In younger plants the stipe scar and costa 
are nearer the angle and in older plants they are farther 
away (pl. 66, f. 7-9). 
In structure the plant is made up primarily of an upper 
and a lower plate of epidermal tissue, each composed of a 
single layer of cells. The plates are united at the margins 
of the frond and connected in the interior by walls of 
upright cylindrical cells (pl. 65, f. 7). These walls are 
but one cell thick and one cell high toward the margin 
* Hegelmaier: Die Lemnaceen, t. iv. f. 31, 32 — (1868); Fl. Bras. 
fasc. 76, pl. I. f. iii. f. 1, 2, 4, 5 — (1878). 
