A. B. Rendle. — Najadaceae. k 



Najas graminea is exceptional in having no spathe around the male flower (Fig. 5 S). 

 The adult flowers generally stand singly in the fertile sheath-axil, more rarelj several 

 together, a fertile shoot with suppressed internodes standing in the axil. They are generally 

 2 to 3 mm long. The q? consistsof a sessile or subsessile anther closely surrounded by a 

 thin membranous perianth ending above the anther in two thickened lips (Fig. \ C). The 

 anther is ellipsoidal or oblong in shape, has a delieate wall of two cell-layers and is 

 generally 4- more rarely 1-locular. The cells are crowded with pollen-grains, oval or 

 roundish in shape, both sometimes occurring in one anther, as in N. graminea] the grain 

 has a single delieate uneuticularized wall, more or less Jilled with dark cell-contents con- 

 sisting largely of starch-granules. In N. graminea the perianth forms two large ear-shaped 

 lips above the anther. 



The membranous spathe conforms to the outline of the flower but is prolonged above 

 it into a cylindrical neck which ends in a few of the characteristic spine-cells (Fig. \ G^F). 

 A very short peduncle may be developed below the spathe; in N. podostemon it is almost 

 as long as the flower. Before dehiscence of the anther the flower-stalk elongates pushing 

 the anther, still closely enveloped by the perianth, through the spathe which becomes split, 

 sometimes laterally, sometimes from the apex downwards. The lips of the perianth separate 

 and the anther dehisces apically. 



The female flowers (Fig. \ B) are generally naked, consisting of a somewhat ellipsoidal 

 ovary bearing a narrow style which divides into 2, more rarely 3, equal or unequal, linear- 

 tapering stigmas. In some American species non-stigmatic spine-bearing appendages also 

 oecur. Thus in N. flexilis a pair of spine-arms altern ates with the stigmas (Fig. \ H). 

 N. microdon shows great variety in the number of stigmas and spine-arms, the oecurrence 

 of transitional struetures indicating that the latter are merely barren stigmas. 



In a few tropical old-world species the female flower is enveloped in a spathe closely 

 resembling that of the male. 



Pollination (Befruchtung). As the flowers are always submerged pollination must be 

 effected by passive falling of the pollen , or by the transport of the pollen by currents of 

 water or by aquatic animals. There is no evidence of the last-named. Magnus has observed 

 the grains in N. marina to germinate before leaving the anther, the wall growing out into 

 a long pollen-tube. Jönsson suggests that as the male flowers in monoecious forms stand 

 higher on the shoot than the female which are mature at the same time, the pollen grains 

 fall, weighted by their starch-contents , on to the stigmas beneath. This is quite possible 

 especially as the spathe frequently splits laterally the anther being extruded on a curved 

 pedicel. 



Fruit and Seed (Frucht und Same). The fruit is narrowly ellipsoidal or oblong, 

 enveloped, where this oecurs, in the persistent spathe, and bearing the remains of style and 

 stigmas. In fresh speeimens of N. marina and N. graminea the pericarp was sueculent, 

 when dry the wall becomes thin and membranous generally clinging so closely to the seed 

 as to take the impressions of the pitting on the testa. The seed has a conspieuous raphe. 

 The testa is hard and brittle. In N. marina (Fig. 3 / — Q) it has many layers of cells with 

 hard thick pitted walls , surrounded on the outside by a row of very large cells with thin 

 walls and clear Contents the side walls having a delieate reticulate thickening. The outer 

 cells ultimately perish and the testa consists of a stone-parenehyma, the surface of which 

 is rugulose with irregulär polygonal pittings. Its thickness varies in the different forms and 

 varieties. In the other species there are only three layers. The cells of the innermost are 

 thickened and flattened, those of the middle layer are more nearly isodiametric with very 

 thick hard much pitted walls , while those of the outer show three forms of development. 

 In N. flexilis and N. tenuissima they are thickwalled and the seed-coat is smooth and 

 polished. In the commonest type [N. minor, N. graminea etc.) the cells of the outer layer 

 are large, clear, and thin-walled with a delieate spiral thickening on the side-walls. The 

 cells vary in shape in different species giving the characteristic areolation to the testa. In 



