HALORAGEAE 433 



Vanhoffen states that the species flowers and fruits normally in Greenland 

 between 6o and 70 N. lat. (Abromeit, ' Bot. Ergeb. von Drygalski's Gronlandsexped.,' 

 p. 12). 



289. Gunnera L. 



1025. G. manicata Linden. (Jonas, ' Uber d. Inflores. u. Bl. v. Gunnera 

 manicata,' Inaug.-Dissert., Breslau, 1892.) Jonas describes this species as gyno- 

 monoecious. Nectaries are absent. The hermaphrodite flowers are anemophilous, 

 and they alone set ripe fruits. 



290. Callitriche L. 



This genus includes inconspicuous monoecious species; anemophilous and 

 protogynous so far as my own observations go, but generally described as entomo- 

 philous or hydrophilous in some instances. 



1026. C. vernalis Kuetz. (Knuth, 'Bl. u. Insekt. a. d. nordfr. Ins.,' p. 72.) 

 This species is anemophilous and obviously protogynous in the North Frisian 

 Islands, for pollen remains clinging to the anthers of the male flowers when the 

 female ones in the same plant have already set fruits. I have not observed the early 

 stages of anthesis. 



1027. C. stagnalis Scop. (Axell, ' Om Anord. for Fanerog. Vaxt. Befrukt.,' 

 p. 36; Knuth, op. cit, p. 72; Hegelmaier, 'Monographic d. Gatt. Callitriche,' 

 Stuttgart, 1864 ; Ludwig, Kosmos, Stuttgart, x, 1881-2, p. 32 ; Warnstorf, Verh. bot. 

 Ver., Berlin, xxxviii, 1896.) In the North Frisian Islands this species also is 

 anemophilous and protogynous. Hegelmaier describes the flowers as anemophilous, 

 but also says they are protandrous, the male flowers maturing before the female 

 ones of the same inflorescence. The former are mostly situated in the axils of 

 the upper leaves, and the latter in those of the lower ones. The pollen-grains are 

 covered with a thick, somewhat tuberculated membrane. 



Ludwig says that in this species and the other Eucallitricheae (C. vernalis and 

 C. hamulata) the fibrous anther-layer characteristic of aerial flowers is present, a 

 layer which plays an important part in dehiscence. He describes the stamens as 

 i mm. long, with stiff filaments, and producing pollen-grains about 25 p long 

 and 2 1 fi broad. The two styles are almost entirely covered with papillae. 



Besides aerial flowers Ludwig also observed submerged ones, fertilized under 

 the surface of the water. Hegelmaier found such flowers to be infertile, and Kerner 

 says that their anthers do not usually dehisce, but decay with the pollen they contain. 

 The flowers of terrestrial stocks growing in mud or damp woods behave like those 

 of aquatic ones. 



Warnstorf describes the flower mechanism of the variety (a) vera Aschs. some- 

 what as follows. Owing to the extreme shortening of the terminal nodes of the 

 shoots, the opposite leaves are crowded into a floating rosette. The diclinous 

 (monoecious) flowers are situated in their axils. As a rule the female flowers 

 first make their appearance. The two long styles are beset with stigmatic papillae 

 for two-thirds of their length, and project for about 3 mm. beyond the leaves of 

 the rosette. After pollination and elongation of the nodes the flowers become sub- 

 merged and ripen their fruits. At a later stage the male flowers appear in their 



DAVIS. II p f 



