{iv} An English translation of the ‘Lehrbuch der Botanik’ by Professor Sachs, has recently (1875), appeared under the title of ‘Text-Book of Botany,’ and this is a great boon to all lovers of natural science in England. {1a} ‘Proc. Amer. Acad. of Arts and Sciences,’ vol. iv. Aug. 12, 1858, p. 98. {1b} Ludwig H. Palm, ‘Ueber das Winden der Pflanzen;’ Hugo von Mohl, ‘Ueber den Bau und des Winden der Ranken und Schlingpflanzen,’ 1827. Palm’s Treatise was published only a few weeks before Mohl’s. See also ‘The Vegetable Cell’ (translated by Henfrey), by H. von Mohl, p. 147 to end. {1c} “Des Mouvements révolutife Respontanés,” &c., ‘Comptes Rendus,’ tom. xvii. (1843) p. 989; “Recherches sur la Volubilité des Tiges,” &c., tom. xix. (1844) p. 295. {8} ‘Bull. Bot Soc. de France,’ tom. v. 1858, p. 356. {9a} This whole subject has been ably discussed and explained by H. de Vries, ‘Arbeiten des Bot. Instituts in Würzburg,’ Heft iii. pp. 331, 336. See also Sachs (‘Text-Book of Botany,’ English translation, 1875, p. 770), who concludes “that torsion is the result of growth continuing in the outer layers after it has ceased or begun to cease in the inner layers.” {9b} Professor Asa Gray has remarked to me, in a letter, that in _Thuja occidentalis_ the twisting of the bark is very conspicuous. The twist is generally to the right of the observer; but, in noticing about a hundred trunks, four or five were observed to be twisted in an opposite direction. The Spanish chestnut is often much twisted: there is an interesting article on this subject in the ‘Scottish Farmer,’ 1865, p. 833. {10} It is well known that the stems of many plants occasionally become spirally twisted in a monstrous manner; and after my paper was read before the Linnean Society, Dr. Maxwell Masters remarked to me in a letter that “some of these cases, if not all, are dependent upon some obstacle or resistance to their upward growth.” This conclusion agrees with what I have said about the twisting of stems, which have twined round rugged supports; but does not preclude the twisting being of service to the plant by giving greater rigidity to the stem. {12} The view that the revolving movement or nutation of the stems of twining plants is due to growth is that advanced by Sachs and H. de Vries; and the truth of this view is proved by their excellent observations. {14} The mechanism by which the end of the shoot remains hooked appears to be a difficult and complex problem, discussed by Dr. H. de Vries (ibid. p. 337): he concludes that “it depends on the relation between the rapidity of torsion and the rapidity of nutation.” {16} Dr. H. de Vries also has shown (ibid. p. 321 and 325) by a better method than that employed by me, that the stems of twining plants are not irritable, and that the cause of their winding up a support is exactly what I have described. {17} Dr. H. de Vries states (ibid. p. 322) that the stem of Cuscuta is irritable like a tendril.