{34} Prof. Asa Gray informs me that the tendrils of P. sicyoides revolve even at a quicker rate than those of P. gracilis; four revolutions were completed (the temperature varying from 88 degrees- 92 degrees Fahr.) in the following times, 40 m., 45 m., 38.5 m., and 46 m. One half-revolution was performed in 15 m. {35} See M. Isid. Leon in Bull. Soc. Bot. de France, tom. v. 1858, p. 650. Dr. H. de Vries points out (p. 306) that I have overlooked, in the first edition of this essay, the following sentence by Mohl: "After a tendril has caught a support, it begins in some days to wind into a spire, which, since the tendril is made fast at both extremities, must of necessity be in some places to the right, in others to the left." But I am not surprised that this brief sentence, without any further explanation did not attract my attention. {36} Sachs, however ('Text-Book of Botany,' Eng. Translation, 1875, p. 280), has shown that which I overlooked, namely, that the tendrils of different species are adapted to clasp supports of different thicknesses. He further shows that after a tendril has clasped a support it subsequently tightens its hold. {37} Annales des Sc.