260 Excerpta Botanica. 



Blume, to the inflorescence of the Aroidece, of which the Lem- 

 nacea 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- 

 nacece be carefully examined, they will be found to constitute 

 the lowest group of the Aroidece, 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. 



AROIDE^E. 



Trib. Lemnace^e, DC. 



Herbula liberae, natantes vel submersse, arrhizse, vel 1-poly-rhiza?, 

 radicibus calyptra* terminatis. Vasaspiralia 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: bulbillusf autumno fundum aquae, vere 

 superficiem petens. Infiorescentia : spadix ob axim suppressum 

 fere nullus ; spatha urceolata, membranacea : staminum evolu- 

 tione irregulariter fissa. Flares 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. 



f 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 tli« Lemnacece, 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 Lemnacece) ; — is truly denominated a Bulbillus. 



