232 



or sixes, 5-6 mm. long, not decayed at the tips. Often monoe- 

 cious, the flowers consisting of a single stamen or a single pistil ; 

 sometimes all the flowers in the axils of the whorls staminate. 

 Stamens as long as the ripe fruit ; filaments thick : anthers 

 large. Fruit almost oval, minutely granulated, a little over i 

 mm. in length ; the persistent style shorter than the nutlet. 



Turfy places in Siberia, Alaska and the Selkirk Mountains, 

 British Columbia (Macoun). 



2. Callitriche. L. Sp. PI. 969. (1753). 



Widely dispersed over the earth in warm and temperate cli- 

 mates. As usually reckoned, it numbers about twenty species, 

 one half of them occurring in the United States. In some cases, 

 however, the species run so close to each other that they can be 

 distinguished only by fruit markings. In this paper Hegelmaier's 

 classification of our North American forms is retained more for 

 the sake of avoiding the creation of new synonyms than for any 

 other reason. A stricter grouping would probably throw C. verna, 

 C. stenocarpa, and C. Bolanderi into one. It is doubtful, too, if 

 C. verna and C. JieteropJiylla should be considered as distinct 

 species, since they can be separated only by the fruit, and are 

 constantly confounded. Each of them, also, varies more or less 

 in the shape of the fruit, so that it is not always easy to place the 

 specimens. 



The leaves of most or all the species are covered on 

 both sides with dark, colored dots termed by Engelman 

 " stellate scales, " and by Hegelmaier " stellate hairs. " Under 

 the microscope they appear to be composed of a dark ring in 

 which is a slightly sunken disc with a minute cell in the centre 

 from which radiate lines dividing the disc into several cells. 

 They are more numerous in the aquatic than in the terrestrial 

 species, in the former usually having four cell divisions, and 

 in the latter eight, or sometimes split into twice as many 

 divisions. 



Authors have generally regarded the flowers as monoecious, 

 calling the stamens and pistils separate flowers, although they 

 may stand side by side in the same axil and enclosed in the same 

 perigonium. In respect to this I am bound to say that I agree 



