LEMNA TRISULCA. IVY-LEAVED DUCKWEED.
L EMNA trisulca ; frondibus teneris elliptico-lanceolatis basi caudatis apice serratis, radicibus solitariis.
L EMNA trisulca. Linn. Sp. PI. p. 1376. L ig h tf. Scot. p. 537. Huds. Angl. p, 399. With. Bot. A rr. cd. 4.
m l. 2. p. 43. Hoffm. Germ. ed. 2. ml. 1. P . I I. p. 186/ Willd. Sp. P L ml. 4. p. 193. Smith
FI. B r it. p. 957. Engl. Bot. t. 926. Decand. FI. Fr. ed. 3. ml. 2. p. 589. FI. Gall. Syn. p. 119.
Wahl. Lapp. p. 222. Svensk Bot. t. 324. f . 4. Alton Hort. Kew. ed. 2. ml. 5. p . 233. Pers. Syn.
P I. m l. 2. p. 532. Hook. FI. Scot. P . I. p. 10.
H Y D RO PH A C E caule filiformi, foliis elliptico-lanceolatis, viviparis. Hall. Helv. n. 1901.
L EN T ICU LA aquatica trisulca. R ail Syn. p . 129-
L EN T ICU LA R IA ramosa monorrhiza, foliis oblongis, pediculis longioribus donatis. Micheli N ov. Gen. p. 16.
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Class a n d Order. D IA N D R IA MONOGYNIA.
[Natural Order. AROIDEÆ.—N AYAD ES, Juss. Decand.—HYDROCHARIDIBUS A FEIN IS, Brown.']
Gen. Char. Perianthium simplex,, monophyllum, membranaceum, urceolatum. Fructus : Capsula vel Utriculus monolocularis.
Gen . Char. Perianth single, monophyllous, membranaceous, urceolate. Fruit, a Capsule.br Utricle of 1 cell.
Radix : fibra solitaria. pellucida filiformis uncialis vel ultra,
ad apicem çalyptrata.
Frondes natalités, semiunciam vel fere unciam long®, virides,
pellucid®, fere membranaceæ,/eticulatæ, elliptico- seu
ovato-lanceolatæ, basi in caudamvel petiolum tenuem
product», apice magis minusve acute serrât», medium
versus, in utrumque marginem, rima longitudinali gem-
mifera vel flprifera. Iiæ gemmce cito explanat» sunt
in frondes novellas cruciatim dispositas, multoties proliféras.
Flos minutus, solitarius, plerumque hermaphroditus, raro dioi-
cus.
Perianthium liberum, simplex, membranaceum, pelluci-
dum, reticulatum, fere albidum, urceolatum, demum
hinc longi tudinali ter ruptum.
Stamina, ubi advint, duo, ad latus inferius germinis recepta-
culo inserta. Filamenta pistillo longiora, alba. An-
theroe flav», rotundat®* didymæ, loculis verticaliter de-
hiscentibus. Pollen flavum, granulis rotundatis, mu-
ricatis.
PlSTlLLUM : Germen subrotundatum, supra planum, subtus
carinatum. Stylus longitudine germinis, sursum cur-
vatus. Stigma paululüm expansura, planum.
PERIGARPIUM : Utriculus rotundato-reniformis, hinc de-
pressus, basi styli terminatus : extus cellulosus, intus
crüstaceus.
SEMEN oblongo-ellipticum, longitydinaliter positum, latere inferiore
affixum. . ; ’ ‘
Albumen copiosum, carnosum.
Embryo oblongus, medium versus paululum Constrictus, se-
minis difectionë.
Root : a solitary filiform pellucid fibre an inch or more long,
calyptrate at the extremity.
Fronds natant, half an inch or nearly an inch long, green,
pellucid, almost membranaceous, reticulated, elliptical-
or ovato-lanceolate, produced at the base into a slender
tail or petiole, at the extremity more or less serrated,
towards the middle, on each margin, having a longitudinal
cleft which bears either gemm® or flowers.
These gemma are soon developed into new fronds disposed
cross-wise, and are many times proliferous.
Flower minute, solitary, generally perfect, rarely dioecious.
Perianth free, simple, membranaceous, pellucid, reticulated,
almost white, urceolate, at length opening longitudinally
on one side.
Stamens, when present, two, inserted, upon the receptacle, on
the lower side of the germen. Filaments longer than
the pistil, white. Anthers yellow, roundish, didy
mous, the cells opening vertically. Pollen yellow, the
granules roundish, muricated.
Pistil : Germen roundish, plane above, keeled beneath.
Style'as long as the germen, curved upwards. Stigma
a little spreading, plane.
Pericarp : a Utricle of a roundish reniform shape, depressed
on one side, terminated with the'base of the
style: externally cellular, internally crustaceous.
Seed oblongo-elliptic, placed longitudinally, fixed by its lower
surface.
Albumen abundant, fleshy.
Embryo oblong, contracted near the middle, having the same
f - direction as the seed.
Fig. 1, 1, 1. Gemmiferous and proliferous fronds. Fig. 2. Frond in flower, nat. size. Fig. 3, 3. Gemmiferous and proliferous
fronds. Fig. 4. Gemma. Fig. 5, 5, 5. Flowering fronds. Fig. 6. Frond bearing fruit. Fig. 7. Flower seen from
the under side. Fig. 8. Flower destitute of perianth, seen from the upper side. Fig% 9- Female flower. Fig. 10. Ovule.
Fig. 11. Ovule cut open. Fig. 12. Utricle. Fig. 13. Utricle and seed cut through vertically. Fig. 14. Perianth from
which the external pulpy substance is removed. Fig. 15. The same cut through transversely, showing the albumen and
embryo. Fig. 16. Embryo.— all more or less magnified.
A Qerman author, of the name of Wolf, who published a dissertation upon the genus Lemna, is said by Sir James Smith
in Rees’s Cyclopedia, to have been the first person who discovered the flowers of this curious though not uncommon species.
His work was printed at A ltorf in 1801, in the June of which year Mr. Dawson Turner claimed the honour o f being
the first to detect the flowers of Lemna trisulca in Great Britain. They were discovered near Y armouth; but from the neighbourhood
of London numerous specimens have been sent to me a t various times between the months of June and September
by Mr. Graves, from which, they being in different stages o f fructification, the accompanying drawing was made.
So many and striking are the peculiarities which attend all the species of Lemna, as to distinguish them at first sight from
all the other known genera of plants. The whole plant may truly be said to consist of a frond, since there is no distinction
between the stem and leaves. The individuals float upon the surface of the water, collected together in great masses, affording
harbour for various species of aquatic insects, and are the food (as the common English name denotes) of ducks, and
many water-birds. From the centre of the under side of the fronds, descend solitary, or clustered, simple fibres or radicles,
which never reach so low as to strike into the earth, but are terminated by a distinct sheath, resembling the calyptra of a
moss. Their most common mode of increase is by gemm®, which are produced, generally singly, in marginal clefts, seen on
each side near the base of the leaf. These, even while remaining in the clefts, expand into perfect plants, which, without separating
themselves from that frond which gave them birth, do again (in the present species more particularly ) bear other fronds,
and so on for a number of generations.
The structure of the flowers is no less curious than the mode of increase of the fronds which I have now described. These
are produced singly in a lateral cleft similar to that which bears the gemm®. A solitary pistil is mostly accompanied by two
anthers, and surrounded by a membranous urceolate covering, which has been usually considered a perianth {Calyx or Corolla),
Bor an artificial system, merely, such a view of the structure might suffice. But Mr. Brown has satisfied bimseif,
from recent and accurate examinations of the fruit, that this genus should be placed among the natural order of Aroidece ; and
a close attention to the form of the flower, as well as of the fruit, will be found to warrant this conclusion: Were this plant
truly diandrous, the two stamens would be seen to be placed on each side of the germen ; they would not advance progressively
: here, on the contrary, they are placed both on one side, and both beneath the germen, and are not seen both in perfection
at the same period. The receptacle, though not lengthened out as in most o f the Aroidece, is nevertheless to be looked
upon as a spadix, and the pistil and two anthers as so many distinct naked flowers which it produces; the whole being
surrounded by a'spatha (the Calyx or Corolla o f authors).
Mr. Lindley, author of a Monograph of the Genus Rosa and a more recent and splendid work on the genus Digitalis,
considers the Lemna to belong to the third section of Aroidece ( Fructus capsularis) of Humboldt and Kunth’s Nova Genera
et Species Plantarum ( Pistiacece of Richard), and as such I have published it in the Flora Scotica,
With regard to the point of insertion of the seed, it is a t the centre of the lower surface; but there is an appearance of a
seedstalk intimately connected with the seed itself which .runs along to one extremity, where is perhaps the true hilum: at the
other extremity I have always observed the seed to be lodged in a purplish-brown fleshy mass, which forms a sort of operculum,
and which I do not recollect to have seen in any other fruit.
I think to have understood that both Mr. Brown and Mr. Lindley have Seen a minute cleft in the embryo, which the former
gentleman discovered also in the genus Arum.
In ditches and other stagnant waters this species of Lemna is far from uncommon. Mr. Brown has mentioned it as a native
of New Holland.