In the chapter on the Sleep of Plants the conspicuous circumnutation of Marsilea quadrifoliata (Marsileaceae, Fam. 4) will be described.

It has also been shown in Chap.  I. that a very young Selaginella (Lycopodiaceae, Fam. 6), only .4 inch in height, plainly circumnutated; we may therefore conclude that older plants, whilst growing, would do the same.

Fig. 120.  Lunularia vulgaris:  circumnutation of a frond, traced from 9 A.M.  Oct 25th to 8 A.M. 27th.

(35.) Lunularia vulgaris (Hepaticae, Fam. 11, Muscales).—­The earth in an old flower-pot was coated with this plant, bearing gemmae.  A highly inclined frond, which projected .3 inch above the soil and was .4 inch in breadth, was selected for observation.  A glass hair of extreme tenuity, .75 inch in length, with its end whitened, was cemented with shellac to the frond at right angles to its breadth; and a white stick with a minute black spot was driven into the soil close behind the end of the hair.  The white end could be accurately brought into a line with the black spot, and dots could thus be successively made on the vertical glass-plate in front.  Any movement of the frond would of course be exhibited and increased by the long glass hair; and the black spot was placed so close behind the end of the hair, relatively to the distance of the glass-plate in front, that the movement of the end was magnified about 40 times.  Nevertheless, we are convinced that our tracing gives a fairly faithful representation of the movements of the frond.  In the intervals between each observation, the plant was covered by a small bell-glass.  The frond, as already stated, [page 259] was highly inclined, and the pot stood in front of a north-east window.  During the five first days the frond moved downwards or became less inclined; and the long line which was traced was strongly zigzag, with loops occasionally formed or nearly formed; and this indicated circumnutation.  Whether the sinking was due to epinastic growth, or apheliotropism, we do not know.  As the sinking was slight on the fifth day, a new tracing was begun on the sixth day (Oct. 25th), and was continued for 47 h.; it is here given (Fig. 120).  Another tracing was made on the next day (27th) and the frond was found to be still circumnutating, for during 14 h. 30 m. it changed its course completely (besides minor changes) 10 times.  It was casually observed for two more days, and was seen to be continually moving.

The lowest members of the vegetable series, the Thallogens, apparently circumnutate.  If an Oscillaria be watched under the microscope, it may be seen to describe circles about every 40 seconds.  After it has bent to one side, the tip first begins to bend back to the opposite side and then the whole filament curves over in the same direction.  Hofmeister* has given a minute account of the curious, but less regular though constant, movements of Spirogyra:  during 2 ½ h. the filament moved 4 times to the left and 3 times to the right, and he refers to a movement at right angles to the above.  The tip moved at the rate of about 0.1 mm. in five minutes.  He compares the movement with the nutation of the higher plants.** We shall hereafter see that heliotropic movements result from modified circumnutation, and as unicellular Moulds bend to the light we may infer that they also circumnutate.]