287 



CCLVIII. FLUVIALES. 



Naiades, Juss. Gen. 18. (1789) in part.— Fluviai.es, Vent. Tabl. 2. 80. (1799).— Potamo- 

 philje, Rich. Anal. Fr. (1808).— Potame.k, Juss. Diet. Sc. Nat. 43. 93. J1826); Dec. and 

 Duby, 439. (1828).— Naide*, Agardh Aph. 125. (1822).— Fluviales, Rick. Mem. Mus. 

 1. 364. (1815) ; Lindl. Synops.24Q. (1829).— Hydrogetones, Link Handb. 1. 282.(1829.)— 

 Naide^e, lb. 1. 820. (1829.) 



Diagnosis. Caulescent floating exalbuminous monocotyledons, with a slit 

 embryo, definite stamens, and dry superior fruit with pendulous seeds. 



Anomalies. Caulinia and some others are said to have no spiral vessels. 



Essential Character. — Flowers monoclinous or diclinous, Periantkium of 2 or 4 pieces, 

 often deciduous, rarely wanting-. Stamens definite, hypogynous. Ovarium I or more, supe- 

 rior ; stigma simple ; ovule solitary, pendulous. Fruit dry, not opening-, 1-celled, 1-seeded. 

 iSeed pendulous ; albumen none ; emoryo antitropous, with a lateral cleft for the emission of 

 the plumula. — Water-plants. Leaves very cellular, with parallel veins. Flowers inconspicuous, 

 usually arranged in terminal spikes. 



Affinities. In this order we have the nearest approach, except in Pistia- 

 ceae, to the division of flowerless plants. The perianthium is reduced to a few 

 imperfect scales, the habit is almost that of Conifers, and there is, in some of 

 the genera either a total absence of spiral vessels, or that form of tissue exists 

 in a very rudimentary state. Pollini asserts, according to Decandolle (Org. 

 Veg. 40), that spiral vessels do exist in them ; but Amici, on the other hand, 

 maintains that there is no trace of them, at least in Caulinia. Ann. des Sc. 2. 

 42. The manifest affinity of Fluviales to Juncagineas determines a relation on 

 the part of the former to Aroidese, which is confirmed by the tendency to pro- 

 duce a rudimentary spatha in some of them, and by their undoubted resem- 

 blance to Pistiaceas, which may be understood as reduced Aroideee. It is re- 

 markable that Adanson was aware of this relationship between Aroideae and 

 Fluviales, to which, however, Jussieu, whose Naiades are a very heterogene- 

 ous assemblage, did not assent. They are generally translucent cellular plants, 

 destitute of stomata, having no epidermoidal layer, and perishing rapidly upon 

 exposure to air. M. Amici has seen the sap circulate in the transparent joints 

 of Caulinia fragilis, which he states is the unknown plant upon which Corti 

 made observations relating to the same subject. See Amici in Ann. des Sc. 2. 

 42. Agardh refers to this order both Ceratophyllum and Sparganium. 



Geography. Common in extra-tropical countries, but also found near the 

 equator. Potamogetons are in every ditch and swamp as far north as Iceland. 



Properties. Very unimportant. The root of Potamogeton natans is said 

 to be eaten in Siberia, and that of Aponogeton distachyum by Hottentots. 

 Zostera, or Sea wrack, is a common material for packing, and for stuffing cot- 

 tagers' cushions. 



Examples. Naias, Zostera, Caulinia, Cymodocea, Thalassia, Ruppia, 

 Zannichellia, Potamogeton. 



CCLIX. JUNCAGINE^E. 



Juncagineji, Rick. Anal. Fr. (1808) ; Mem. Mus. 1. 364. (1815) ; Lindl. Synops. 252. (1829) ; 

 Dec. and Duby, 438. (1828). a sect, of Alismaceae. 



Diagnosis. Caulescent exalbuminous monocotyledons, with a slit embryo, 

 6 stamens, and dry superior fruit with erect seeds. 



