The land plants of the salt-marsh, as well as the aquatic species, furnish interesting examples of overlap with the sea flora, but a brief reference must suffice. The Glasswort (_Salicornia_), for instance, has furnished itself with a very complete equipment for the difficult conditions of salt-marsh life (see pp. 17, 18), and grows far out on the mud-flats in green colonies, often below the upper limit of the Bladder-wrack or _Fucus_, the common brown Seaweed of our shores. The Glasswort has discarded leaves, its stems have become thick and succulent, and its flowers, reduced to the minutest and simplest dimensions, are almost buried in the fleshy branches. Thus armed, it braves the salt-desert of the mud-flats, and repeated submersion by the tides leaves it uninjured. Under the peculiar conditions of its life, it relies neither on insects nor wind nor water for pollination, the flowers being self-pollinated. A more surprising commingling is that which is illustrated by A. D. Cotton in his report on the Seaweeds of the Clare Island district (_Proc. Royal Irish Academy_, vol. xxxi., 1912), where, on peaty soil a little above mean high-tide level, the Sea Pink is shown forming a sward with a peculiar dwarf form of _Fucus_ (_F. vesiculosus_, var. _muscoides_) and a few other salt-marsh Seed Plants, such as _Schlerochloa_ (_Glyceria_), _Glaux_, _Salicornia_. The Sea Pink is highly evolved florally, and differs widely from the Saltwort in its abundant production of leaves and showy flowers, the absence of any conspicuous xerophile characters, and the fact that it is not confined to the coasts, being often a member of the alpine flora of our higher hills. In its association with _Fucus_ it may be claimed that it is the latter which is “out of water,” as it never produces fruit, increasing solely by means of vegetative growth. At the same time, so closely does it press its partner in the struggle for room, that the Sea Pink fails to form its usual robust clumps, its stem being mostly unbranched and its stature dwarfed.
Viewing generally the migration of the Seed Plants from land to water, we see that the fresh waters of the world, untenanted by other large plants, have been fully colonized, generally a long time ago, and by plants of rather early types. But as regards the sea, the luxuriant Algal vegetation which is in possession of our shores has no reason to tremble for its supremacy. Beautifully adapted for their life, whether in sheltered bays or on stormy rocks, the Seaweeds show no sign of relinquishing the domain that has been theirs since the earliest rocks which still display traces of organic life were laid down in Cambrian seas.