PETALOIDE^, 



389 



ILLUSTRATIVE GENERA. 



Actinocarpus, JK. Br. 

 Sagittaria, L. 



Subord. 3. BUTOMEJE. Internal 

 circle of perianth coloured : ovules 

 numerous all over the inner surface 

 of the carpels ; embryo curved. 



Butomus , Tournef. 

 Limnocharis, H. fy B. 



Subord. 1. JUNCAGINE^E. Peri- 

 anth scaly ; anthers always extrorse ; 

 ovule inverted; embryo straight. 



Triglochin, L. 



Scheuchzeria, L. 



Subord. 2. ALISMEJE. Internal 

 circle, of the perianth coloured; ovules 

 solitary or twin ; ovule and embryo 

 curved. 



Alisma, Juss. 



Affinities, &c. The Alismece bear considerable resemblance to the Dico- 

 tyledonous Order Ranunculaceae, while Butomece have been compared 

 with the Nymphaeaceae on account of the curious placentation ; but there 

 is hardly any real relationship in this latter case. On the other hand, the 

 Alismece have some similarity to the Commelynacese, from which they are 

 separated by the aperispermic seed. This structure of the seed agrees 

 with that of Naiadaceae, with which this Order is connected by the Jun- 

 cayinece. Scheuchzeria in this last division approaches Juncaceae. 



Distribution. A small group, the members of which inhabit marshy 

 localities in all parts of the world ; most abundant, perhaps, in temperate 

 climates. 



Qualities and Uses. An acrid property is common in the foh'age and 

 in the rhizomes, but the latter are sometimes fleshy and farinaceous, and 

 then may be eaten after the acridity is removed by cooking. Sagittaria 

 sinensis is cultivated for food in China. Many are very handsome aquatic 

 plants, and are cultivated for the sake of their flowers. 



NAIAD ACE^E. THE POND-WEED 'ORDER. 



Coh. Potamales, HooTt. 



Diagnosis. Immersed aquatic plants, with jointed 

 sheathing stipules within the petioles, or with 

 sheathing bases to the leaves ; inconspicuous, 

 monoecious, dioecious, or perfect flowers, which 

 are naked or have a free, scale-like perianth ; the 

 ovaries solitary or 2-4 and distinct, 1-celled, 1- 

 ovuled; seed aperispermic; embryo straight or 

 curved (fig. 474), with a thin membranous testa. 

 Illustrative Genera : Naias, Willd. ; Zostera, L. ; 

 Ruppia, L. ; Zannichellia, Michel. ; Potamogeton, 

 L. ; Aponogeton, Thunb. 



stems and 

 Fig. 474. 



geton, with the testa 

 removed : a, radicle ; 

 6, cotyledon ; c, plu- 

 mule. 



Affinities, &c. This Order agrees with Hydrocharidaceae and Alismaceas 

 the structure of its seeds, but differs in the 



simpler organization of the 



