31i DR HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 



treat the distribution of vulgaris, Br., str'icta, Audrz., and arcuata Reich., in connexion. A. 

 Gray considers the American stricta and arcuata as varieties of vulgaris. Bentham says that 

 B. vulgaris, prcecox, and stricta pass through every gradation into one another. Another 

 element of confusion in this group is the doubtful origin of the common pot-herb B. prce- 

 cox. "Watson treats it as an alien. Torrey and Gray, on the other hand, describe it as a 

 native of Canada, ascending to 68° N., though perhaps stricta is here meant, for A. Gray 

 latterly refers prcecox of Fl. Bor.-Am. to vulgaris, var. stricta, and riglitly as far as the 

 specimens I have examined go to show. Tries remarks (Summa, p. 1-16) that Smith's 

 ovigmvil prcecox (Flora Britannica) is a cultivated arcuata, the English Botany plant being 

 diflPerent (thus accounting for Ny man's conclusions above stated). My North Indian and 

 Himalayan Barbareas are, again, generally referable to the European forms, though 

 scarcely characteristic of them. I long endeavoured to keep the Australian and New 

 Zealand form distinct ; but neither Bentham nor Mueller regard it as different from vul- 

 garis, with which undoubted wild specimens from the Australian Alps well accord. 



TuEMTis ^;a^?«^rt, Graham, and retrofracta, Hook., are, I think, identical with T. mollis, 

 Hook. The Arabis Holbollii, Horn., is another synonym. There are certainly differences 

 in the length and breadth of the pod in both patula and retrofracta ; but these do not at 

 all indicate the seeds being in one or two rows, which is a very variable character in both. 

 Arabis IlolbdlUi is identified with A. retrofracta, Grab., by Lange. 



AiiABis lyrata, DC. This, which is the Sisymbrium humifusum, J. Vahl, and Arabis 

 sisymbrioides, Hook., differs according to descriptions from A. petnea, Lamk., in the rather 

 oblique radicle of the embryo, and biennial root (Torrey and Gray, i. 80, 81), neither of 

 which characters appear to me to hold good in the rather numerous specimens I have 

 examined, the radicle being in both variable as to direction, and the roots identical. In 

 habit and every other respect, the plants entirely accord, as far as herbarium specimens 

 allow me to judge. According to Eries, A. petrcea is not a native of Lapland; nor does 

 Ledebour give any European or Asiatic arctic habitat for it ; it is, however, common in 

 Finland, Scandinavia, Iceland, and N. Britain. Eries includes A. ambigua, DC, under 

 it, a plant kept distinct by Ledebour and by Torrey and Gray. 



Cakbamine bellidifolia , L. I have sometimes been almost disposed to suspect that 

 this may be an arctic form of hirsuta, to which it certainly is very closely allied, and to 

 which it tends through microphylla, Willd. C. Lenensis is identical with bellidifolia, and 

 is var. Lenensis, Trautv. (Elorula Taimyr.). 



C. hirsuta, L. This, though a common Icelandic plant, and one that crosses the circle 

 in America, does not occur in Scandinavia north of Gothland and Finland. The C. sylva- 

 tica, Link, is distinguished by its six stamens, spreading pedicels, and style as long as the 

 siliqua is broad, — all variable characters, except that of the stamens. In the southern 

 hemisphere and elsewliere C. hirsuta is hexandrous. Watson finds no difficulty in distin- 

 guishing these as wild plants in England, but considers sylvatica a doubtful species, 

 adding that the distinctions are less decided under cultivation. Bentham considers sylva- 

 tica to be a large luxuriant hexandrous form of hirsuta. 



C. digitata, Bich. I have examined a large suite of excellent flowering specimens of 



