it would be sufficient to observe the stems in about a score of genera, belonging to widely distinct families and inhabitants of various countries.  Several plants [page 202] were selected which, from being woody, or for other reasons, seemed the least likely to circumnutate.  The observations and the diagrams were made in the manner described in the Introduction.  Plants in pots were subjected to a proper temperature, and whilst being observed, were kept either in darkness or were feebly illuminated from above.  They are arranged in the order adopted by Hooker in Le Maout and Decaisne’s ‘System of Botany.’  The number of the family to which each genus belongs is appended, as this serves to show the place of each in the series.

[(1.) Iberis umbellata (Cruciferae, Fam. 14).—­The movement of the stem of a young plant, 4 inches in height, consisting of four internodes (the hypocotyl included) besides a large bud

Fig. 70.  Iberis umbellata:  circumnutation of stem of young plant, traced from 8.30 A.M.  Sept. 13th to same hour on following morning.  Distance of summit of stem beneath the horizontal glass 7.6 inches.  Diagram reduced to half of original size.  Movement as here shown magnified between 4 and 5 times.

on the summit, was traced, as here shown, during 24 h. (Fig. 70).  As far as we could judge the uppermost inch alone of the stem circumnutated, and this in a simple manner.  The movement was slow, and the rate very unequal at different times.  In part of its course an irregular ellipse, or rather triangle, was completed in 6 h. 30 m.

(2.) Brassica oleracea (Cruciferae).—­A very young plant, bearing three leaves, of which the longest was only three-quarters of an inch in length, was placed under a microscope, furnished with an eye-piece micrometer, and the tip of the largest leaf was [page 203] found to be in constant movement.  It crossed five divisions of the micrometer, that is, 1/100th of an inch, in 6 m. 20 s.  There could hardly be a doubt that it was the stem which chiefly moved, for the tip did not get quickly out of focus; and this would have occurred had the movement been confined to the leaf, which moves up or down in nearly the same vertical plane.

(3.) Linum usitatissimum (Lineae, Fam. 39).—­The stems of this plant, shortly before the flowering period, are stated by Fritz Müller (’Jenaische Zeitschrift,’ B. v. p. 137) to revolve, or circumnutate.

(4.) Pelargonium zonale (Geraniaceae, Fam. 47).—­A young plant, 7 ½ inches in height, was observed in the usual manner; but, in order to see the bead at the end of the glass filament

Fig. 71.  Pelargonium zonale:  circumnutation of stem of young plant, feebly illuminated from above.  Movement of bead magnified about 11 times; traced on a horizontal glass from noon on March 9th to 8 A.M. on the 11th.