810 



XXII. NAIADES. 



Zostera. 



Embryo cut vertically, and portion of 



cotyledon, showing the point. 



Zostera marina. 



Pistil laid open below to show the insertion of the 



ovule (mag.). 



Zostera. 



Fruit, entire and opened 



(mag.). 



Zostera. 



Embryo, entire and cut transversely 



(mag.). 



sub- globular or ovoid; testa tbin or membranous, smootb or reticulate. Embryo 

 macropodous. 



Zostera. 

 Halophila. 



Phucagrostis. 

 Posidonia. 



GENERA. 



Lemnopsis. 



Najas. 



Phyllospadix. 



Caulinia. 



Zostera inhabits the estuaries of the Norlh Sea and Atlantic and Indian Oceans, Posidonia unA Phuca- 

 f/rostis the Mediterranean, and Phylhspadix the western shores of North America. Caulinia and Najas 

 inhabit fresh still waters in Europe and America. In Holland the leaves of Zostera are used in the con- 

 struction of dykes. For some years they have been used in France for stuffing mattresses and for packing. 



Adrien de Jussieu, who studied the classification of Monocotyledons, divided them into albuminous 

 and exalbuminous, and the latter again into terrestrial (Orclndece) and aquatic. The exalbuminous 

 aquatics have been divided into two sections, according to the presence or absence of a true perianth. 

 The cUamydeous- section includes Alismacecs, Butomece, snA. Sydrocharideep, y^YAch have six perianth 

 divisions, the three inner petaloid; the other section comprises Jvncagivecs, Naiadeee, Potametp, and 

 Zosteracea, which have a scaly, membranous, or herbaceous perianth, or are achlamydeous. The three 

 families of the first section are distinguished by free or coherent ovaries, and by the placentation ; those 

 of the second section by the embryo, which is brachypodous and homotropous in Jvncni/ivcce, macropodous 

 and antitropous in Zosteracea, macropodous and amphitropous in Potamecs, macropodous and homotropous 

 in NaiadecB. 



"With modifications we have adopted this classification,' and after many endeavours we have suc- 

 ceeded in uniting in what appear to us homogeneous groups, the exalbuminous aquatic Monocotyledonous 

 genera, placed in one family by most botanists. Without overlooking the close afiinity between Jimca- 

 ginets, Potamem, Naiadece, &c., we think that the form of the stigmas — entire and peltate, or divided and 

 pointed — may serve to group very naturally the different genera of NaiadetP, and Potamees, the latter bein"' 



' After many attempts by many botanists, it is 

 pretty clear that any linear arrangement of the Mono- 

 cotyledonous families is quite impossible, and that there 

 is little choice between several of them ; under which cir- 



stances the simplest and most practical is that adopted 

 in this work. See Synopsis of Orders at the end. — 

 En. 



