260 Excerpta Botanica. 
Blume, to the inflorescence of the Aroidee, of which the Lem- 
naceeé are a tribe. 
If it be at all proper to establish a genus on characters de- 
rived from the vegetation, he feels himself justified in the 
adoption of his genus Spirodela. For, if the whole of the Lem- 
naceé be carefully examined, they will be found to constitute 
the lowest group of the Aroidee, and a very slight sagacity 
will detect in them a series of well-defined developments pro- 
ceeding from Wolffia (which is probably the simplest phane- 
rogamic plant) up to Spirodela, which presents the highest 
state of organization, and is evidently the connecting link 
with Pistia. The sudden appearance of two stipular leaves 
which must be regarded as typical of the stipular sheath of 
Pistia, the surprising development of spiral vessels, with- 
out any visible change in the exterior form of the plant and 
of the axis which is easily distinguishable as a node with 
many roots, furnish in these simple plants characters suffi- 
ciently important to justify the establishment of a particular 
genus ; and probably a more attentive examination of the fe- 
male organs and of the fruit may elucidate other characters 
confirmatory of this genus on the above grounds, however ar- 
bitrary its adoption may at present appear. 
AROIDEE. 
Trib. Lemnacea, DC. 
Herbule libere, natantes vel submerse, arrhizz, vel 1-poly-rhize, 
radicibus calyptra* terminatis. Vasa spiralia rudimentaria trans- 
itoria (in pistillo) vel conspicua (in tota planta). Axis ad 
punctum reductus, cum foliis in frondem confluens. Frons: 
singula planta completa, ex rima una basilari, vel duabus late- 
ralibus prolifera, prole nuda, vel stipulis duabus membranaceis 
aucta. Hibernaculum: bulbillus + autumno fundum aque, vere 
superficiem petens. IJnflorescentia: spadix ob axim suppressum 
feré nullus; spatha urceolata, membranacea: staminum eyolu- 
tione irregulariter fissa. Flores monoici. Masc. 1—2, mon- 
* The calyptra is not a loose portion of the epidermis, nor a distorted form 
of the radical spongiole, but is a proper and peculiar organ, which surrounds 
the apex of the root even whilst it lies concealed in the plant, although per- 
fectly free and distinct both from that and from the parenchyma. 
+ Definition of a bulbillus: an axillary bud, the parts of which are more 
fleshy than usual, and connate, and which separates spontaneously from 
the parent plant for the purpose of propagating the species. A more 
fleshy frond, therefore, without roots, engendered in the autumn by plants 
of the Lemnacee@, and on the death of the parent plant separating from it 
and seeking the bottom of the pit, the parent plant remaining on the sur- 
face of the water (as in Lemna polyrhiza), or becoming buried in the 
bottom of the water with its dead parent plant, and rising again in spring 
(as in the rest of the Lemnacee) ;—is truly denominated a Bulbillus. 
