Fig. 94.  Glaucium luteum:  circumnutation of young leaf, traced from 9.30 A.M.  June 14th to 8.30 A.M. 16th.  Tracing not much magnified, as apex of leaf stood only 5 ½ inches from the glass.

(3.) Crambe maritima (Cruciferae, Fam. 14).—­A leaf 9 ½ inches in length on a plant not growing vigorously was first observed.  Its apex was in constant movement, but this could hardly be traced, from being so small in extent.  The apex, however, certainly changed its course at least 6 times in the course of 14 h.  A more vigorous young plant, bearing only 4 leaves, was then selected, and a filament was affixed to the midrib of the third leaf from the base, which, with the petiole, was 5 inches in length.  The leaf stood up almost vertically, but the tip [page 229] was deflected, so that the filament projected almost horizontally, and its movements were traced during 48 h. on a vertical glass as shown in the accompanying figure (Fig. 95).  We here plainly see that the leaf was continually circumnutating; but the proper periodicity of its movements was disturbed by its being only dimly illuminated from above through a double skylight.  We infer that this was the case, because two leaves on plants growing out of doors, had their angles above the horizon measured in the middle of the day and at 9 to about 10 P.M. on successive nights, and they were found at this latter hour to have risen by an average angle of 9o above their mid-day position:  on the following morning they fell to their former position.  Now it may be observed in the diagram that the leaf rose during the second night, so that it stood at 6.40 A.M. higher than at 10.20 P.M. on the preceding night; and this may be attributed to the leaf adjusting itself to the dim light, coming exclusively from above.

Fig. 95.  Crambe maritima:  circumnutation of leaf, disturbed by being insufficiently illuminated from above, traced from 7.50 A.M.  June 23rd to 8 A.M. 25th.  Apex of leaf 15 1/4 inches from the vertical glass, so that the tracing was much magnified, but is here reduced to one-fourth of original scale.

(4.) Brassica oleracea (Cruciferae).—­Hofmeister and Batalin* state that the leaves of the cabbage rise at night, and fall by day.  We covered a young plant, bearing 8 leaves, under a large bell-glass, placing it in the same position with respect to the

* ‘Flora,’ 1873, p. 437. [page 230]

light in which it had long remained, and a filament was fixed at the distance of .4 of an inch from the apex of a young leaf nearly 4 inches in length.  Its movements were then traced during three days, but the tracing is not worth giving.  The leaf fell during the whole morning, and rose in the evening and during the early part of the night.  The ascending and descending lines did not coincide, so that an irregular ellipse was formed each 24 h.  The basal part of the midrib did not move, as was ascertained by measuring at successive periods the angle which it formed with the horizon, so that the movement was confined to the terminal portion of the leaf, which moved through an angle of 11o in the course of 24 h., and the distance travelled by the apex, up and down, was between .8 and .9 of an inch.