iv THE LESSON OF THE BRITISH FLORA 35 



marshes on the coast of the United States, occur also in the 

 interior of the continent in the vicinity of salt-springs. 



Facts of this sort are well known, and I merely refer to them 

 here in order to emphasise the importance of this little group 

 of British littoral plants, those of the salt marsh. Their very wide 

 distribution is connected with the frequent recurrence of suitable 

 conditions, not only in space, but what seems of greater import, 

 also in time. One can scarcely doubt when the Saltwort (Salsola 

 kali) is seen on the Devonshire coast, on a beach in Chile, and in 

 the elevated regions of Central Asia that here a very ancient type 

 of plant finds its still more ancient conditions of existence. In the 

 capacity which most of the plants of the salt marsh possess of 

 germinating in sea-water, this group of littoral plants is sharply 

 distinguished, as far as my observations show, from the other 

 groups of British shore-plants. For instance, in my experiments 

 the seeds of Aster tripolium, Salicornia herbacea, and Triglochin 

 maritimum germinated freely in sea-water, whilst those of Sper- 

 gularia rubra, Cakile maritima, Convolvulus soldanella and others 

 failed to do so^(see Note 19). It will also be noticed with 

 respect to this group of littoral plants that, except in the case of 

 Scirpus maritimus, the seeds or fruits have little or no floating 

 power, the exception offered by Salsola kali being not very striking. 

 This feature is brought out in the Table given in Note 10 ; but 

 some of the details of my observations are given in Note 17. 



There yet remains a third group of the British shore-plants, 

 namely, that comprising the plants that rarely stray far from the 

 beach and often possess seeds or seedvessels that will float for 

 months. Here we have such species as Arenaria (Honckeneya) 

 peploides, Beta maritima, Cakile maritima, Crambe maritima, Crith- 

 mum maritimum, Convolvulus soldanella, Eryngium maritimum, 

 Euphorbia paralias, Glaucium luteum, Lathyrus maritimus, Poly- 

 gonum maritimum, &c. The seeds or seedvessels of quite half 

 of these species will float for months unharmed in sea-water, but 

 in a few, as with Cakile maritima and Eryngium maritimum, they 

 float for only a week or two, whilst in others again like Glaucium 

 luteum they have no buoyancy. (Some details of the buoyancy 

 experiments on these plants are given in Note 18 ; and the long 

 list in Note 10 may be first consulted.) 



It is not necessary to enter here into more detail with respect to 

 British shore-plants. Enough has been said to disclose cleavage- 

 lines in what might have appeared as a homogeneous plant-forma- 

 tion. We can thus discern the elements of at least three groups 



D 2 



