6 A. B. Rendle. — Najadaceae. 



a third type (e. g. N. microdon) ' the outer and side-walls of the outer layer are not thick- 

 ened, but collapse, while the inner wall becomes thickened and with its concave surface 

 forms the shallow pits, rows of which give a characteristic marking to the coat. 



The straight embryo fills the testa. It consists of a large hypocotyl and radicle, a 

 well-developed lateral plumule and a blunt terminal cotyledon. 



Geographica! Distribution (Geographische Verbreitung). Najas is almost world- 



wide occurring in all zones except the frigid. It is still unrecorded for certain areas in which 

 it might be expected to occur, such as Tasmania and New Zealand. The genus consists of a 

 few widely distributed and a number of apparently more or less local species. N. marina, 

 a Polymorphie species, comprising the subgenus Eunajas , oecurs over almost the whole 

 area of the genus but finds its chief development in the north temperate zone of the Old 

 World. The subgenus Caulinia has no such widely distributed species. N. minor ranges 

 from the south of Europe and the Mediterranean area to tropical Africa and eastwards to 

 India, North Asia and Japan; it has a variety in Scandinavia. N. graminea is an Old World 

 tropical and subtropical species. N flexilis is temperate North American and North West 

 European ; N. microdon replaces it in the warmer parts of America. The remaining species 

 have all restricted areas and fall for the most part into small geographical groups, namery 

 an Asiatic, Australian, Mascarene, African, and West Indian and tropical South American. 



Systematic Relations (Verwandtschaftliche Beziehungen). Najas forms a distinet 

 and apparently primitive type of Monocotyledon. Its place is undoubtedly in the Helobiae 

 series of which it has the characteristic large macropodous embryo. Its nearest ally is 

 Zannichellia which resembles it in the axial stamen and the female inflorescence ; the 

 latter is quite comparable but contains several flowers within the spathe. In general 

 vegetative strueture Najas strongly resembles several submerged genera of Hydrociiariteae 

 (Lagarosijihon, Hydrilla and Elodea) with slender branching stems, crowded narrow 

 sessile leaves and an often finely toothed leaf-margin, the flowers being also enveloped by 

 a tubulär or sac-like spathe but showing much higher differentiation. 



Fossils (Fossile Reste). Heer has described 3 species from tertiary strata namely 

 N. effugita and stylosa from Oeningen and N. striata from Spitzbergen. The determinations 

 are however extremely doubtful. Undoubted fruits of typical N. marina have been found in 

 various neolithic, interglacial, and preglacial deposits by G. Reid proving the species to have 

 been formerly widely distributed over the Southern portion of England (Fig. 3L). Fruits 

 are also reported from similar deposits in Scandinavia (G. Andersson) and central Europe 

 (G. A. Weber). Fruits of N. flexilis have been recorded from North Germany and Scandinavia 

 indicating that this species was formerly more widely spread than at present in northern 

 Europe. iV. minor (Fig. 4 T) is only known from Britain in fossil fruits found by Reid 

 in Sussex (pleistocene) and Norfolk (Cromer forest bed, preglacial). In the Sussex locality 

 was also found a Single seed of N. graminea (Fig. 5 U), a tropical and subtropical old- 

 world species which has been introduced into North Italy and to one locality in the north 

 of England. 



Genus unicum. 



Najas l. 



Najas [L. Gen. ed. 1. (1737) 278] L. Spec. pl. ed. 1. (1753) 1015; Endl. Gen. (1837) 

 n. 1656; Benth. et Hook. f. Gen. III. (1883) 1018; Magnus in Engl. u. Prantl , Pflzfam. 

 II. 1. (1889) 217. — Cavolinia Raf. in Amer. Monthly Magaz. (1818) 175. — Cavoliuun. 

 Raf. in Journ. de phys. LXXXIX. (1819) 259. — Caulinia Willd. in Mem. Acad. Berlin 1 798 

 (1801) 87. — Fluvialis [J. Bauhin, Hist. pl. III. (1651) 779] Adans. Fam. II. (1763) 472; 

 Pers. Synops. II. (1807) 530. — Fums Tourn. Inst. Herb. I. (1700) 569; Mappus, Hist. 



