14 
I, 
' Limnafitlieminn lacunosum has a slender, ascending or horizontal 
rootstock provided with fleshy, fibrous roots, (Fig. 4). At the grow- 
ing end of the rhizoma we first notice, above the sandy bottom of the 
lake or pond, a few of the submersed leaves described above (si)* 
Their petioles are inserted by means of sheathing bases (Fig. 5, si). 
Next, in centripetal order, we find growing on the rootstock some 
very long filiform petioles of uniform thickness and appearance (Fig. 
4, pi)^ likewise provided with sheathing bases (Fig. 5, //), and 
bearing the roundish floating blades with a deep acute-angled sinus. 
None of these undoubted petioles shows any sign of an inflorescence- 
After removing the sheathing petiole-bases, we see some mem- 
branaceous scales about lo™™' long, which taper from a broad clasp- 
ing base to a sharp point (Figs. 4 and 5, sc). Occasionally these 
scales are more elongated and have green tips or even rudimentary 
blades; they are, in fact, much reduced leaves. 
From the axils of the scales grow those organs which are 
described by authors as filiform petioles beariiig near their summit 
the umbel of flowers, etc. (Fig. 4, st). As we shall presently see, 
they bear lateral organs; therefore, I do not hesitate to consider 
them as caulomes, and will henceforth call them stems. They are, 
indeed, very much like the filiform petioles metioned above, but 
from those they are readily distinguished by their position in the 
axils of the scales, by their somewhat flattened, but never clasping 
base (Fig. 5, j/), and, above all, by their internal structure, to be 
discussed hereafter. 
A short distance from the surface of the water (sf), each stem 
bears a well developed node, from which one full-grown floating leaf 
is produced. The blade of this leaf is exactly like those of the 
leaves with filiform petioles, but its petiole is only from i to 5™* long 
(in one exceptional case as long as 2/^"^^), rather thicker than the 
stem, and has, at its base, a membranaceous sheath from which the 
clustered inflorescence and, closely above the same, the apex of the 
main axis are growing. This apex, however, rarely continues its 
growth vigorously during the same season; but we can often observe 
very small rudimentary leaves starting at this point, during and after 
the flowering season (Fig. 4) * 
The apex of the stem is usually subtended by a cluster of spur- 
shaped, thick and fleshy rootlets (not tubers, as they are called by 
some authors), (Fig. 4, sp, and Fig. 7.) There can be no doubt 
that these rootlets sink to the bottom at the end of the growing sea- 
son carrying with them the apex of the stem, which, in the next 
spi'ing, gives rise to a new plant. I have frequently found these 
rootlets attached to the rootstock of young as well as older plants, 
itidicating, in the latter case, by their withered and shrunken con- 
dition, the: function which they had performed (Fig. 6). 
We see from what I have said above that in Z. lacunostm we 
meet with four distinct kinds of leaf-organs: ist, the submersed 
♦According to A. Gray (Manual) the long petioles sometimes shoot forth neW 
leaves from near the spur-like roots, thus spreading by a sort of proliterou* 
