Empetrum.] LXIX. EMPETRACE^E. 397 



stamens of the males protruding from the perianth on slender filaments. 

 Fruit black, globular, about the size of a pea. 



In mountain heaths and bogs, in Europe, Asia, and North America, 

 very abundant at high northern and Arctic latitudes, and quite alpine in 

 southern Europe and central Asia, and a red-berried variety abounds in 

 the Falkland Islands. Common in Scotland, in northern and western 

 England, and in Ireland. Fl, spring. 



LXX. OALLITRIOHINE^. THE CALLITKICHE 

 FAMILY. 



Aquatic, floating herbs, with opposite or whorled leaves, and 

 minute unisexual flowers in their axils. No perianth. Ovary 

 and fruit either 1-seeded or 4-lobed, with 1 seed in each lobe. 



Two genera, each of a single species. Allied in many respects to 

 Halorageoz, they are sometimes placed next to or amongst them ; but 

 there is no perianth, and they are therefore more frequently enumerated 

 amongst anomalous Monochlamydce. [These genera are regarded by 

 others as forming two families, of which Callitrichinece have been re- 

 ferred both to Euphorbicem and to Haloragece. The position of Cerato- 

 phyllum is quite uncertain.] 



I. CERATOPHYLLUM. HORNWORT. 



Leaves whorled and dissected. Stamens several. Style 1. Ovary 

 and fruit entire, with a single seed. 



1. C. demersum, Linn. (fig. 901). Hornwort. — A glabrous perennial, 

 the stems floating like those of a Myriophyllum, and the leaves are 

 whorled in the same manner, but instead of being pinnately divided 

 they are twice or thrice forked, with linear often fine and subulate seg- 

 ments, usually slightly toothed on the edge. Flowers small, sessile in 

 the axils of the leaves, each one surrounded by a whorl of minute bracts, 

 but without any real perianth ; the males consisting of 12 to 20 sessile 

 oblong anthers, the females of a small ovary with a simple style. Fruit 

 an ovoid, slightly compressed nut, 2 to 3 lines long, either two sharp 

 species (0. demersum proper), or with a few tubercles or prickles (C. sub- 

 mersum, 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. Fl. summer, but only in 

 shallow water. 



II. CALLITRICHE. CALLITRIOHE. 



Leaves opposite entire. Stamens solitary. Styles 2. Ovary and fruit 

 4-lobed and 4-seeded. 



1. 0. aquatica, Sm. (fig. 902). Common O. or Water Stanvort—A 

 glabrous, slender perennial, either floating in water or creeping and root- 

 ing 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 



