Prakger — The Buoyancy of the Seeds of some Britannic Plants. 51 



my own samples sank in a few days. Gruppy notes that these two species 

 vary as regards buoyancy. 



Fapaveraceae. 

 Species tested, 8. All sink at once. 



Cntciferae. 

 Species tested, 49. The seeds of all sink at once, save for those of 

 Matlhiola incana, Radicula Nasturtium-aquaticum, N. palustre, and Barharea 

 lymta, of which N. palustre alone floated for over a week. The dried fruit 

 of Cramhe, Bapkanus Raphanistrum, and R. maritimus possesses considerable 

 buoyancy, though their seeds have none. 



Viotaceae. 

 Eight species of Viola were tested ; all floated for a few hours or days. 



Caroyph ijltaceae. 

 Species tested, 41. All sank at once, except Honlienya, the seeds of 

 which floated (in fresh water) for 2 days. As regards this plant Guppy 

 (/. c, p. 541) gives a period of 10 days (and " a week or two " after a year's 

 drying) for these seeds in fresh water, but found that, in salt water, 75 per cent, 

 were still afloat after a year's immersion. The plant supplies an interesting 

 exception to the rule that seeds which sink in fresh water sink also after 

 a slightly longer period in salt water. 



Ht/pericaceae. 

 Species tested, 11. Floating power slight, varying from (the usual 

 condition) to 1 day. 



Geraiiiaceae. 



Species tested, 15. All sink at once. 



Lefjtuninosae. 

 Species tested, 49. The seeds of all sink at once, except those of Anthyllis 

 Vulneraria (1 day), and Onobrychis viciaefolia (21 days). But the fruit of 

 several Medicks and of Trifolium arvense floated for a few days, and these 

 form the usual dispersal-unit of the species in question. 



Rosaceae. 

 Species tested, 37. The fruits vary greatly in character, and are 

 very variable in floating power, even within the same genus. The only 

 species with apparently indefinite floating power are Gomarum palustre 

 (the only marsh-plant of the series) and Potentilla Anserina; Spiraea Ulmaria 

 and Agrimonia Eupatoria follow with 1| and 1 month. The behaviour of 



