There is scarce a chain-length of the shores of Britain and Ireland that has not been a hundred and a hundred times explored by the botanist,—keen to collect and prompt to register every rarity of the vegetable kingdom; but has he ever yet succeeded in transferring to his herbarium a single plant caught in the transition state? Nay, are there any of the laws under which the vegetable kingdom exists better known than those laws which fix certain species of the algæ to certain zones of coast, in which each, according to the overlying depth of water and the nature of the bottom, finds the only habitat in which it can exist? The rough-stemmed tangle (_Laminaria digitata_) can exist no higher on the shore than the low line of ebb during stream-tides; the smooth-stemmed tangle (_Laminaria saccharina_) flourishes along an inner belt, partially uncovered during the ebbs of the larger neaps; the forked and cracker kelp-weeds (_Fucus serratus_ and _Fucus nodosus_) thrive in a zone still less deeply covered by water, and which even the lower neaps expose. And at least one other species of kelp-weed, the _Fucus vesiculosus_, occurs in a zone higher still, though, as it creeps upwards on the rocky beach, it loses its characteristic bladders, and becomes short and narrow of frond. The thick brown tufts of _Fucus canaliculatus_, which in the lower and middle reaches of the Lake of Stennis I found heaped up in great abundance along the shores, also rises high on rocky beaches,—so high in some instances, that during neap-tides it remains uncovered by the water for days together. If, as is not uncommon, there be an escape of land springs along the beach, there may be found, where the fresh water oozes out through the sand and gravel, an upper terminal zone of the confervæ, chiefly of a green color, mixed with the ribbon-like green layer, (_Ulva latissima_,) the purplish-brown layer, (_Porphyra laciniata_,) and still more largely with the green silky Enteromorpha, (_E. compressa_.)[37] And then, decidedly within the line of the storm-beaches of winter,—not unfrequently in low sheltered bays, such as the Bay of Udale or of Nigg, where the ripple of every higher flood washes,—we may find the vegetation of the land—represented by the sentinels and picquets of its outposts—coming down, as if to meet with the higher-growing plants of the sea. In salt marshes the two vegetations may be seen, if I may so express myself, _dovetailed_ together at their edges,—at least one species of club-rush (_Scirpus maritimus_) and the common saltwort and glasswort (_Salsola kali_ and _Salicornia procumbens_) encroaching so far upon the sea as to mingle with a thinly-scattered and sorely-diminished fucus,—that bladderless variety of the _Fucus vesiculosus_ to which I have already referred, and which may be detected in such localities, shooting forth its minute brown fronds from the pebbles. On rocky coasts, where springs of fresh water come trickling down along the