5 and 6 P.M.  On the next day the leaf stood at only 10o above the horizon at 8.25 A.M., and it remained at about 15o till past 3 P.M.; at 5.40 P.M. it was 23o, and at 9.30 P.M. 58o; so that the rise was more sudden this evening than on the previous one, and the difference in the angle amounted to 48o.  The movement is obviously periodical, and as the leaf stood on the first night at 55o, and on the second night at 58o above the horizon, it appeared very steeply inclined.  This case, as we shall see in a future chapter, ought perhaps to have been included under the head of sleeping plants.

(33.) Pontederia (sp.?) (from the highlands of St. Catharina,

Fig. 118.  Pontederia (sp.?):  circumnutation of leaf, traced from 4.50 P.M.  July 2nd to 10.15 A.M. 4th.  Apex of leaf 16 ½ inches from the vertical glass, so tracing greatly magnified.  Temp. about 17o C., and therefore rather too low.

Brazil) (Pontederiaceae, Fam. 46).—­A filament was fixed across the apex of a moderately young leaf, 7 ½ inches in height, and its movements were traced during 42 ½ h. (see Fig. 118).  On the first evening, when the tracing was begun, and during the night, the leaf descended considerably.  On the next morning it ascended in a strongly marked zigzag line, and descended again in the evening and during the night.  The movement, therefore, seems to be periodic, but some doubt is thrown on this conclusion, because another leaf, 8 inches in height, appearing older and standing more highly inclined, behaved differently.  During the first 12 h. it circumnutated over a [page 257] small space, but during the night and the whole following day it ascended in the same general direction; the ascent being effected by repeated up and down well-pronounced oscillations.

Cryptogams.

(34.) Nephrodium molle (Filices, Fam. 1).—­A filament was fixed near the apex of a young frond of this Fern, 17 inches in height, which was not as yet fully uncurled; and its movements were traced during 24 h.  We see in Fig. 119 that it

Fig. 119.  Nephrodium molle:  circumnutation of rachis, traced from 9.15 A.M.  May 28th to 9 A.M. 29th.  Figure here given two-thirds of original scale.

plainly circumnutated.  The movement was not greatly magnified as the frond was placed near to the vertical glass, and would probably have been greater and more rapid had the day been warmer.  For the plant was brought out of a warm greenhouse and observed under a skylight, where the temperature was between 15o and 16o C. We have seen in Chap.  I. that a frond of this Fern, as yet only slightly lobed and with a rachis only .23 inch in height, plainly circumnutated.*

* Mr. Loomis and Prof.  Asa Gray have described (’Botanical Gazette,’ 1880, pp. 27, 43), an extremely curious case of movement in the fronds, but only in the fruiting fronds, of Asplenium trichomanes.  They move almost as rapidly as the little leaflets of Desmodium gyrans, alternately backwards and forwards through from 20 to 40 degrees, in a plane at right angles to that of the frond.  The apex of the frond describes “a long and very narrow ellipse,” so that it circumnutates.  But the movement differs from ordinary [[page 258]] circumnutation as it occurs only when the plant is exposed to the light; even artificial light “is sufficient to excite motion for a few minutes.” [page 258]