56 Scientific Proceedings, Royal Dublin Society. 



GuUuiii. — The only marsh species, G. falastre, floats for months. Five 

 other species sink within a day. 



Artemisia. — A. onaritima floats for over a week. A. Ahsinthium and A. 

 vulgaris sink at once. 



Senecio. — S. aquaticus and apparently S. palustris display a buoyancy not 

 above the low average of the genus. 



Stachys. — 8. 'palustris floats for many months. The other three British 

 species sink within a day. 



Runiex. — R. eonglomeratus, R. sanguineus, B. Hydrolapathum, and R. erispus 

 are far more buoyant than R. pulc/ier, R. obtusif alius, R. aquaticus, R. Acetosa, 

 R. Aeetosella. 



Polygonum. — P. Roberti floats for over a month ; P. Hydropiper for a week ; 

 9 other species, including P. maritimmn and P. minus, for a few days only 

 or not at all. 



Uuphorbia. — E. Paralias floats for a month or two (Guppy ; only a few 

 days in my specimens) ; eight other species, including E. portlandiea, for a few 

 days or not at all. 



Jtmcus. — Buoyancy nil, save for IJ day in the case of J. acutus. 



Scirpus. — Buoyancy very low, variable. 



Carex. — Already commented on (p. 55). 



See also the notes on Natural Orders above. 



In Vicia, Hypericum, Epilobium, Plantago we find no noticeable higher 

 buoyancy in the marsh or maritime species as compared with others. 



It will be seen from these notes and those on Natural Orders, and from 

 the Table, that, while high buoyancy is found mainly in marsh and maritime 

 species, it is not the rule even in these ; exceptions are numerous, and definite 

 relationships do not exist between buoyancy and habitat, or buoyancy and 

 any other character. The only general conclusion that can be drawn is that 

 buoyancy is very seldom found in seeds; it occurs mainly in indehiscent 

 fruits. 



The Case of Fleshy Fruits. 



As pointed out on a previous page, the natural unit of dispersal in the 

 case of fleshy fruits, such as berries or drupes, may be whole fruit, in either a 

 fresh or dried condition ; or it may be the seed or stone freed from its fleshy 

 envelope. Birds are the cause of the scattering of vast numbers of the seeds 

 contained in berries and so on ; these may subsequently get into streams, and 

 aquatic dispersal may follow endozoic dispersal. It is therefore desirable 

 that the buoyancy of such fruits, both fresh and dried, should be tested, in 

 addition to that of the contained seeds. I find my results in this direction 



