390 SYSTEMATIC BOTANY. 



inflorescence, which, as also its perianth, is like that of Spadiciflorae, which, 

 however, is connected with that of Alismacese in Scheuchzeria. Decaisne 

 and Maout, following A. de Jussieu, keep distinct the Juncagineae, Apono- 

 geteae, Potameae, and Naiadeae, all of which, with the exception of the 

 first, are here included under Naiadaceae. The groups established or main- 

 tained by the authors just cited are collectively characterized by the 

 absence of a perianth or at least of a petaloid perianth, while they are 

 separated one from the other by the form and direction of the embryo, 

 which is straight and slender and with the radicle next the hilum 

 in Juncagineee, swollen and with the radicle away from the hilum 

 in Zostera, swollen and with the embryo so curved that both its 

 extremities are near the hilum in Potameee, swollen and with the 

 radicle directed to the hilum in Naiadeae. The form of the stigmas, 

 whether entire and truncate or linear and divided, is also relied 

 oil to distinguish the several groups. Some authors consider the in- 

 florescence really spadiciflorous, and regard the scaly perianth, when 

 present, as consisting of bracts surrounding imperfect unisexual flowers ; 

 and this idea is supported by the spathe-like bract which occurs in some 

 genera (Zostera, c.). From this point of view they are related to Lem- 

 naceae ; but the character of the seeds is diverse. The structure of these 

 plants is generally very simple, consisting chiefly of cellular tissue of very 

 delicate organization ; in Ouvirandra the lamina of the full-grown leaf 

 becomes a delicate lattice-like plate, the interspaces between the ribs being 

 destroyed during expansion. Zostera is remarkable for its pollen-grains 

 being tubular and destitute of an external coat. 



Distribution. The species are numerous, and are met with in still, fresh 

 and brackish water, and in the sea (Zostera*), in all parts of the world. 



Qualities and Uses. Apparently destitute of active properties. The 

 leaves of Zostera marina are collected and dried on the sea-coast as a 

 material for packing, filling mattresses, &c. 



Division II. Spadiciflorae. 



Monocotyledons with flowers usually on more or less fleshy, 

 simple or branched spikes (spadices), with or rarely without spathes. 

 Perianth biseriate ; segments uniform, herbaceous or none. 



Exceptions, &c. This group is one readily recognizable, though not easily 

 defined in words. It is subject to many exceptional and transitional forms. 

 In Palms the structure of the perianth is like that of some Liliaceae or Jun- 

 caceae, but the segments are more fleshy ; the Lemnaceae, usually considered 

 the lowest representatives of the Aroid type, have so few flowers that the 

 spadiciform peduncle does not represent this structure very clearly, but it 

 is surrounded by a spathe. Taccaceae resemble Araceae in habit, but their 

 flowers are more complete. The inflorescence is of the same general cha- 

 racter throughout, but with many modifications. 



