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242 immigrant from the westward. The south of Scotland and England, South Sweden, the western Pyrenees, and Atlantic shores of Spain are its principal European habitats, but it is not found in the vast Russian dominions, in any portions of Asia, or of Sicily, the Eastern Archipelago, or other mediterranean regions. It inhabits all the Atlantic Isles, the Azores and Canaries, and I have gathered it in Madeira, Ascension and St. Helena. In the Tropics and south temperate zone it extends no further east than the Cape and Mauritius, but re-appears in New Holland, according to De Candolle, though it is not mentioned by Brown, nor have I seen it in that country. Erorn the above enumeration it woidd seem that this plant has, to a certain extent, been distributed by the agency of ships, but we are at a loss to conceive, why a species so readily transplanted to inhabited spots, as the Atlantic Islands, should have not been also introduced upon the much frequented coasts of Asia; the disinclination it manifests to proceed by land further east than the shores of those countries which it has so readily gained, is another fact connected with the geographical distribution of the present and some other introduced plants, of which I am unable to offer an explanation.

The last peculiarity of S. pinnalifula to which I would allude, is the comparatively high northern latitude it attains in Europe to what it does in America, where its limit is 32° lower in latitude. This probably arises from the species being impatient of great cold, at any part of the year, the severity of the American winters being, even in North Carolina, very considerable. The same agent, cold, may check in some degree the easterly progress of the plant in the northern States of Em-ope, but certainly not in the southern or mediterranean regions.

7. SISYMBRIUM, Lmn.

1. Sisymbrium Sophia, Linn.; Sp. PL 922. DC. Syst. Teg. vol.i. p. 193. Smith, Engl. Bot. t. 963.

Var. canescens ; siliquis latioribus plerumque brevioribus. S. canescens, auctorum.

Hab. Strait of Magalliaens, Cape Negro ; C. Darwin, Esq.

These specimens agree in every particular with others gathered on the walls of the city of Norwich, except in the siliqua of the latter being rather longer and narrower.

There are two widely distributed, and, especially in the foliage and pubescence, highly variable species of the genus; both of which seem so remarkably to follow civilized man, that it becomes extremely difficult to assign the native place to either. The true S. Sophia is generally considered a European plant only ; but it appears to be truly a native of Canada, according to Torrey and Gray, it also occurs in Mexico, if Galeotti's (no. 4682) be, as I suspect, a mere variety, and I am unable to distinguish some of Dr. Gillies' Chilian specimens from the European. The variety, described above, is a very common American state of S. Sophia, having the siliquae shorter and broader than the European state, to it I refer Mr. Darwin's plant, and that of Dr. Gillies. It also inhabits Valparaiso, Buenos Ayres, and California, from whence however, I have seen but one specimen, with immature fruit. S. ca- nescens, Nutt., has still shorter pods, generally about half as long as the pedicels, and borne upon very long racemes. It is a native of the Andes of Mendoza, of Mexico, California and the United States, and of Cape Farewell on the coast of Patagonia. Though very distinct at first sight, it is not so in reality. The pods are variable in length, particularly the pedicels, for, in both Mexican and Snake-country ( California) specimens, they are considerably shorter than the siliqua?. The »S'. Sophioides, Fischer, which runs along the Arctic sea-shores of Asia and America, must I fear sink into a variety of S. Sophia, or probably a state of that species, altered by the rigorous climate. The pods are certainly longer, but that is a variable character. The Cardamine Menziesii of De Candolle is identical with this. The Sisymbrium millefolium, Ait., of Teneriffe is closely allied to the above, but is very distinct in its large flowers and remarkably woody habit : the leaves are divided into very minute segments, a character to which I do not attach any importance ; Mr. Webb has described it in his admirable "Phytographia Canariensis" under the generic name of Descurainea, which includes also the present species and some other Sisi/mbria.