398 THE CALLITRICHE FAMILY.  [Ceratophyllum. 
(C. submersum, Linn.), either scattered over the surface or united in a 
slightly prominent wing round the edge. 
In pools, slow streams, and shallow margins of lakes, dispersed almost 
all over the globe. Not uncommon in Britain. FV. swmmer, but only 
in shallow water. | 
Il. CALLITRICHE. CALLITRICHE. 
Leave opposite, entire. Stamens solitary. Styles 2. Ovary and fruit 
4-lobed and 4-seeded. 
1, C. aquatica, Sm. (fig. 900). Common Callitriche.—A glabrous, 
slender perennial, either floating in water or creeping and rooting in wet 
mud, flowering young so as to appear annual, varying in length according 
to the depth of the water. Leaves either all obovate or oblong, 1 to 6 
ines long, or the lower submerged ones narrow-linear, and obtuse or notched 
at the top; the upper ones obovate, and spreading in little tufts on the 
surface of the water, or all submerged and linear. Flowers minute, usually 
solitary in each axil, between 2 minute bracts varying much in size and 
sometimes wholly wanting. Male flowers consisting of a single stamen 
with a conspicuous filament; the females of a sessile or stalked ovary, 
with 2 erect or recurved styles. Fruit from 4 to 1 line in diameter, the 
lobes either rounded or keeled or winged on the edge. 
In shallow waters or wet mud, dispersed all over the globe. Abundant 
in Britain. Fl. the whole season. It has been variously divided into from 
2 to about 20 supposed species, from slight differences in the size and form 
of the fruits, the direction of the styles, in the bracts, etc., or from the 
presence or absence of the upper obovate leaves ; but the distinctive charac- 
ters which have been given, all fail when applied to a large number of 
specimens collected in different parts of the world. [The British forms 
generally recognized as species or varieties are six, of which the first five 
have usually floating leaves, bracteate flowers, and the fruit-lobes broadly 
connate. | 
a. C. verna, Linn. (aquatica, Sm.). Fruit subsessile, its lobes turgid, 
sharply keeled. 
b. C. platycarpa, Kuetz. Fruit large, subsessile, its lobes flattish, 
sharply keeled. Often grows prostrate on mud, and is the C. stagnalis, 
Scop. | 
of ©. hamulata, Kuetz. Fruit subsessile, its lobes flattish, shortly broadly 
keeled. 
d. C. obtusangula, Lag. Fruit subsessile, its lobes turgid, back obtusely 
trigonous, 
e. OC. pedunculata, DC. Leaves linear. Fruit sessile or stalked, its 
lobes flattish, sharply keeled. elt 
f. O. autumnalis, Linn. Leaves all submerged and linear, truncate. 
Fruit larger, stalked or sessile, its lobes keeled or winged, connate only at 
the axis. Rare and local. | 
LXXI. URTICACEA, THE NETTLE FAMILY. 
Herbs, or, in exotic genera, trees or shrubs, with leaves 
usually rough or stinging, more or less conspicuous stipules, 
