SPIRODELA. 495 
(opening in June) with shorter and broader lobes, bearing the anthers above their middle. Of the only remaining known 
species of this curious genus Seemann gathered on the Sierra Madre of Mexico a staminate specimen, in bud only, 
which is distinguished from all others by its greater thickness and by the long a of large verticillate 4-parted 
flowers, mostly 6 ina whorl. It may therefire bear the name A, VERTICILLIFLORUM 
IX. SPIRODELA. 
From THE Bonietmn or tHE Torrey Boranicat Cuivs, Vor, I. 1870. 
In reply to a recent communication of specimens, we have received the following letter [42] 
from Dr. Engelmann. Although he thinks the publication unnecessary, we yet venture to print 
it, as he differs from Mr. Aratin in relation to the endopleura, and, of course, the subsequent 
terms of the series. Mr. Austin notified us that he had not had access to his materials for compari- 
son with other species. —~ Editors of the Bulletin. 
Only to-day I finished the examination of your interesting Lemna. As Prof. Hegelmeier, the 
accurate monographer of the family, will no doubt give us a full description and figure of this plant, 
from your specimens, I think it superfluous to try to anticipate him in a much less complete and 
satisfactory manner, but I may say that the fertile fronds are a small, only 24-3} mm. in 
the longer diameter, mostly with 5-6 ribs, or at most 7; and w 5 or sometimes 6 roots. 
Foliaceous organs; spiral vessels (even in the roots), pigment calla and both forms of erystals, 
acicular and glomerate, as in the common form of polyrrhiza; stomata smaller, only 0.14~0.16 mm. 
in larger diameter (whereas in that they are 0.20-0.25 mm. long). — Spathe a complete sac, as in 
Lemna trisulea, gibba, and minor; not a mere circular bract, as in LZ. paucicostata and others. — 
Anthers, 4 mm. in transverse diameter, larger than those of other species, different from those of all 
LIemne (and thus confirming the genus Spirodela), by longitudinal and not transverse dehiscence, as, 
in fact, Hegelmeier already surmises from Griffith’s coarse but reliable figures of the East Indian 
plant. Pollen-grains spinulose, as in the whole family, as often elliptical as globose, 0.018—0.023 mm. 
in the different diameters and sizes; smaller than those of our Lemna paucicostata (0.023—0.027 
mm.). — Pistil, as well as anthers and utricle, strongly dotted with purple (in altohol, brown), sub- 
cuticular cells —ovule, hemitropous; horizontal, as in Z. minor; and, in the 10 or 12 flowers 
now examined, always single; spiral vessels in funiculus, which only occur again in L. gibba, [43] 
in this family; exostome almost closed, while in all others it is open or even (in LZ. paucicostata — 
and perpusilla), incomplete, with the endostome strongly protruding. — Seed horizontal and slightly 
compressed, the dark spot of the chalaza distinctly visible, even through the utricle, and, as in all 
l-ovuled species of Lemna, directed backward to the base of the frond; rhaphe distinct, no spiral 
vessels observed in it; seed (apparently — the specimens examined were not completely matured) 
smooth as in Wolfia, not ribbed as in Lemna ; cellular spongy testa very thick; operculum distinct ; 
endopleura, as usual in Lemne, dark brown, thin; endosperm (albumen) considerable. — Embryo 
cylindric, almost as long as the seed, as usual in the family [what Austin calls albumen “a,” his 
“s” is the starchy afbunten ; o he calls embryo is the plumule]. I take it to be a mostly 1- 
inde’ small form of S. polyrr. 
In all the specimens staat I find the singular circumstance of the first (anterior) stamen 
only being developed and protruding (but never as far as in other species), and the second or pos- 
terior one and the pistil being enclosed. Is this owing to the hour of the day when collected? It 
would be worth while to find out whether in Zemna the first stamen may be developed in the 
morning, and the second at noon or in the afternoon. 
Nov. 13, 1870. 
