28 A NATURALIST IN THE PACIFIC chap. 



The nature of the sorting-process is especially well shown in 

 some of the families, as for instance with the Labiatae. Let the 

 reader put on one side the four species with buoyant fruits, namely,. 

 Lycopus europaeus, Mentha aquatica, Scutellaria galericulata, and 

 Stachys palustris, and on the other side all the species with non- 

 buoyant fruits, such as Salvia verbenaca, Thymus sp., Calamintha 

 officinalis, Nepeta glechoma, N. cataria, Prunella vulgaris, Stachys 

 arvensis, S. betonica, S. sylvatica, Galeopsis tetrahit, Ballota nigra, 

 Lamium purpureum, L. album, Teucrium scorodonia, and Ajuga 

 reptans, and he will at once perceive that he has separated the 

 regular water-side plants from those growing in drier stations. 



If he does the same with the Umbelliferae he will find that 

 when he is separating Hydrocotyle vulgaris, Cicuta virosa, 

 CEnanthe crocata, and Angelica sylvestris from ^Ethusa cynapium, 

 Pastinaca sativa, and Chaerophyllum sylvestre, on account of their 

 buoyant fruits, he is also distinguishing them on account of their 

 stations. On the other hand, there are apparently weighty excep- 

 tions to this rule in the non-buoyancy of the fruits of the three 

 British species of Apium (graveolens, nodiflorum, inundatum), 

 which grow in streams and marshes. Or, again, if we look at the 

 sea-coast representatives of the family, we find that whilst the 

 fruits of the Samphire (Crithmum maritimum) float buoyantly for 

 months, those of Eryngium maritimum seemingly set the law at 

 defiance, and all sink in less than a week or ten days, even after 

 months of drying. To regard these as exceptions, however, is to 

 miss the essential point of the principle concerned. It is not 

 thereby implied that all water-side plants, whether by the sea or 

 by the river or by the pond, have buoyant fruits or seeds, but that 

 nearly all plants with such fruits or seeds have been gathered at 

 the water-side. It will be shown in the next chapter that several 

 other influences go to determine the station of a plant on a beach 

 or by a river. This is true of the Composite, which, if we except 

 our two species of Bidens (cernua and tripartita), come under the 

 play of other determining causes, as indicated by the little or no 

 buoyancy displayed by the fruits of Aster tripolium, Senecio 

 aquaticus, and Carduus palustris. 



Within the limits of a genus we can, however, point to other 

 examples of this principle. Take, for instance, Convolvulus arvensis, 

 the common weed of our fields. Its seeds, whether fresh or dried 

 for months, have no buoyancy. On the other hand, those of 

 Convolvulus soldanella float unharmed in sea-water for half a year 

 and more. Its seeds have come frequently under my notice among 



