HVDRALES.] 



NAIADACEiE. 



U3 



Order XL. NAIADACE^.— Naiads. 



Naiades, Jim. fen. 18. (1789) f«2)a>-<.—Fluviales, Ve7it. Tabl. 2. 80. (1799); Kunth Enum.^.lW.— 

 Potamophilae, Rich. Anal.Fr. (1808).— Potamese, Juss. Diet. Sc. Nat. 43. 93. (1826).— Naiadeae, 

 Affardh Aph. 125. (1822); Endl. gen. Ixxi. 3fei.mer, p. 363.— Fluviales, Ricft. Mim. JWm*. 1.364. 

 (1815).— Hydrogetones, Link. Handb. 1. 282. (1829). 



DiAG.NOSis. — Hydral Endogens, with hypogynous stamens, a free embryo, and globose polle 



Water-plants, inhabiting both the ocean and fresh water. Leaves very celhilar, with 

 parallel veins, and membranous interpetiolar stipules. Flowers inconspicuous, often 

 arranged in terminal spikes, 6 ? . 

 Perianth of 2 or 4 pieces, often de- 

 ciduous, rarely wantmg. Stamens 

 definite, hypogynous. Ovaries 1 or 

 more, superior ; stigma simple ; 

 ovule solitary, pendulous and ortho- 

 tropal or campylotropal, or erect and 

 anatropal. Fruit dry, very rarely 

 opening by regular valves, 1 -celled, 

 1 -seeded. Seed erect or pendulous ; 

 albumen none ; embryo with a 

 greatly enlarged radicle, and a la- 

 tent cleft for the emission of the 

 plumule. 



In this Order we have the nearest 

 approach to the great class of Thal- 

 logens. Many of them live mider 

 water. The perianth is reduced to 

 a few imperfect scales, and there 

 is in some of the genera either a to- 

 tal absence of spiral vessels, or that 

 form of tissue exists in a very rudi- 

 mentary state. Pollini asserts, ac- 

 cording to De CandoUe, that spu'al 

 vessels do exist m them ; but Ami- 

 ci, on the other hand, mamtains 

 that there is no trace of them, at 

 least in Caulinia. The manifest af- 

 finity of Naiads to Arrow-grasses 

 determines a relation on the part 

 of the foi'mer to Arads, which is 

 confirmed by the tendency to pro- 

 duce a rudimentary spathe in some 

 of them, and by their undoubted re- 

 semblance to the Duckweeds. It'is 

 remarkable that Adanson was aware 

 of this relationship between Arads and Naiads, to which, however, Jussieu, whose 

 Naiades are a very heterogeneous assemblage, did not assent. The species of the Order, 

 as now cu'cumscribed, are generally translucent cellular plants, destitute of stomates, 

 having no epidermoidal layer, and perishing rapidly upon exposure to au\ Amici has 

 seen the sap circulate in the transparent joints of Caulinia fragilis, which he states is 

 the unknoAvn plant upon which Corti made observations relating to the same subject. 

 See Amici in Ann. des Sc. 4. 42. Mr. Griffith has remarked that, although the differ- 

 ence between the development of the vegetable carpel leaf and vegetable ovulum is in 

 general sufficiently apparent, an exception has appeared to him to be presented by Naias, 

 in which the future pistil seems to be derived from an annular growth round a central 

 body, which subsequently becomes the ovule ! 



Fig. XCIV. 



Fig. XCIV,— Zannichellia palustria. 1. A flower ; 2. a cluster of ripe ovaries 

 to exhibit the o\iile ; 4. a vertical section of a seed, showing the folded up embryo. 



3. an ovary opened 



