39° ANGIOSPERMAE—DICOTYLEDONES 



says that the stigma secretes nectar and that the flowers are visited by flies. JMy 

 observations show them to be anemophilous, receiving occasional insect-visits. 



2596. E. nigrum L. (Warming, Bot. Tids., Kjobenhavn, xv, 1886, pp. 38-9 ; 

 Knuth, ' Bl. u. Insekt. a. d. nordfr. Ins.,' p. 129.) — The male flowers of this species 

 are pink and possess three stamens, with the vestiges of a pistil. The female 

 flowers are purple, with a short style, and crowned by a black, shining stigma 

 with six to nine rays, and a diameter of 2 mm. Lindman says that they secrete 

 sugar which can be detected by Fehling's solution. 



Besides dioeciously, rarely monoeciously distributed unisexual flowers, Lindman 

 observed occasional protandrous hermaphrodite ones. Warming found the plants 

 in Greenland to be dioecious only, with a majority of male flowers. I have never 

 had an opportunity of observing the plant during anthesis in the North Frisian 

 Islands. Considering its early flowering, the absence of insects at that time (in 

 addition to their scarcity in general in these islands, particularly in April), the 

 frequency of heavy storms just then, and the almost unfailing abundance of fruit- 

 formation in the islands of Sylt, Amrum, and Fohr, I conclude that the species is 

 anemophilous ; on the other hand, the colour of the flowers and the secretion ot 

 nectar by the stigma point to occasional insect-visits, probably of flies. 



Andersson and Hesselman found gynomonoecious plants of this species 

 flowering in Spitzbergen during July (' Bidrag till Kanned. om Spetsbergens o. 

 Beeren Eil. Karlvaxtflora,' pp. 31-2). They have not so far observed ripe fruits, 

 but G. Andersson obtained well-developed ' pips ' in samples of mud from the Mytilus 

 layers of Advent Bay. 



Male, female, and hermaphrodite stocks, and also numerous fruits, have been 

 observed in Greenland (Abromeit, ' Bot. Ergeb. von Drygalski's Gronlandsexped.,' 

 pp. 13-14)- 



Visitors. — Nylander (Finland) observed the bee Colletes cunicularius Z., and 

 Hoppner (Bremen) the bee Andrena convexiuscula K. 



CV. ORDER CERATOPHYLLACEAE GRAY. 



8n. Ceratophyllum L. 



Flowers hydrophilous ; monoecious. 



2597. C. demersum L. (Ludwig, ' Zur Biol. d. phanerog. Siisswasserflora,' 

 pp. 8-1 1 ; Rodier, C.-R. Acad. Sci., Paris, 1877; Beyer, ' D. spont. Beweg. d. 

 Staubgef. u. Stempel' ; Vaucher, 'Hist, physiolog. d. pi. d'Europe,' II, 1841.) — 

 In 1 84 1 Vaucher described the pollination of species of Ceratophyllum by the 

 pollen floating in water as a granular substance ; F. Ludwig's detailed investigations 

 not only confirmed this, but showed that these are the only plants growing in fresh 

 water which are strongly hydrophilous, though there are several such among marine 

 flowering plants. Ludwig summarizes the results of his investigations (op. cit.) 

 somewhat in the following manner. — Male and female flowers are nearly sessile, and 

 occur separately, irregularly arranged in different leaf-whorls, the female ones seeming 

 to predominate below. The male flowers, with abundant stamens and pollen, are 



