Pkaeger — The Buoyancy of the Seeds of some Britannic Plants. 5o 



Cijperaceae. 

 Species tested, 44. It is in the genus Garex that a large proportion of 

 the most buoyant " seeds " are found. The inilated seed-vessel retains its air 

 for indefinite periods, and often keeps the seed afloat till the envelope decays, 

 if germination does not take place in the meantime. Of 29 Oarices tested, 10 

 were still afloat after 15 months' immersion, and 5 more floated for from 1 to 

 12 months. Only one species (C. sylvatica) had a maximum buoyancy- 

 period of less than 1 day. The other genera of Oyperaceae (15 species) are 

 much less buoyant ; 4 of the species tested sank at once, 4 more within a 

 day, 5 more within a week, leaving only Blysmiis (1 month (mihi)), 1-6 

 months (Gruppy), and Cladium (owei 15 months (mihi)), 1-6 months (Guppy). 



Gramineae. 

 The great majority (52 out of 62 species tested) sank with great 

 uniformity in between 1 and 7 days. Five sank in less than a day, and the 

 rest (5 species) in under a month. 



High Buoyancy in Maritime and Marsh Plants. 



Guppy demonstrated from his series of experiments the interesting- 

 fact that almost all the species known to possess considerable seed-buoyancy 

 had their habitat by the sea or on river-sides, and he discusses this 

 question fully (/.c.,pp. 24-39). The same fact comes out prominently in the 

 table on p. 49, in which the plants whose seeds are buoyant are analysed 

 according to their habitats. The remarks above on buoyancy in the 

 leading Natural Orders, point also to the same conclusion. In many genera of 

 which the species occupy a variety of habitats, the fact comes out noticeably 

 that the marsh-dwellers or shore-haunters have a liigher seed-buoyancy than 

 those species which inhabit other situations. But this will be seen to be by 

 no means an invariable rule. The following comments on certain genera bear 

 upon this point : — 



Ranunculus. — Excepting B. parvifloriis, which sinks at once, the loicest 

 buoyancy is found in some aquatic species and in R. Lingua, while those of 

 higher buoyancy include R. Auriconms, R. bulbosus, and R. arvemis. However, 

 R. Flammula has the highest buoyancy of all. 



Zathyrus. — The seeds of L. inaritiinus Qoatior months (Sernander, Norman, 

 Guppy, &c.). Those of five other species sink at once. 



Potentilla. — P. Anserina, also Comarum pahisfre, which is often placed in 



Potentilla, were still afloat after 15 months' immersion. The seeds of six other 



species all sank within 12 hours. 



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