Praegke — The Buoyancy of the Seeds of some Britannic Plants. 49 



The drop from 87 per cent, to 85 per cent, in the final total, as compared 

 with the total in my own experiments, is no doubt due to a fact which 

 Guppy is careful to allow for in his own calculations ; namely, that an undue 

 proportion of plants having a high seed-buoyancy is included in his 

 tables ; which brings us back to near the 90 per cent, long ago estimated 

 by Darwin. 



As regards the balance, which possess the power of floating for periods 

 varying from one week to over fifteen months, an examination of the 

 combined lists fully bears out Guppy's conclusion that the buoyant-seeded 

 plants in our flora are in the main inhabitants of either river-side or sea- 

 shore. If we sub-divide these 133 buoyant species into groups, we may set 

 down twenty-five of them as aquatics, forty-two as marsh-plants, five as bog- 

 plants, seventeen as maritime, while the buoyancy of seven others is due to 

 their fleshy fruits having been dried before testing ; the balance (33 species) 

 is made up mostly of plants of mesophile habitat. We may show this 

 analysis as follows in the percentages of the total for each buoyancy- 

 group : — 



It will be seen that aquatics and marsh-plants claim over half the total, 

 maritime plants one-seventh. Bog-plants are but slightly represented. 

 Dried fleshy fruits (a rare but quite possible dispersal-condition) supply a 

 small contribution to the buoyant list, mainly for the shorter periods The 

 balance of the buoyant seeds is made up of plants differing widely as regards 

 both habit and habitat. 



CAU.SES AND DEGKEES OF BUOYANCY. 



Seeds which possess floating power owe their buoyancy to air which is 

 contained within the outer coverings of the seed (or fruit), and the duration 



