* Dassen,’Tijdschrift vor.  Naturlijke Gesch. en Physiologie,’ 1837, vol. iv. p. 106.  See also Ch.  Royer on the importance of a proper state of turgescence of the cells, in ‘Annal. des Sc.  Nat.  Bot.’ (5th series), ix. 1868, p. 345.

** ‘Beiträge zur Kentniss der Bewegungen,’ etc., in ‘Flora,’ 1879, pp. 42, 43, 67, etc.

*** ‘Annal. des Sc.  Nat.  Bot.’ (5th Series), ix. 1868, p. 366. [page 319]

Tropaeolum, Lupinus, Ipomoea, Abutilon, Siegesbeckia, and probably other genera, it is indispensable that the leaves should be well illuminated during the day in order that they may assume at night a vertical position; and it was probably owing to this cause that seedlings of Chenopodium album and Siegesbeckia orientalis, raised by us during the middle of the winter, though kept at a proper temperature, did not sleep.  Lastly, violent agitation by a strong wind, during a few minutes, of the leaves of Maranta arundinacea (which previously had not been disturbed in the hot-house), prevented their sleeping during the two next nights.

We will now give our observations on sleeping plants, made in the manner described in the Introduction.  The stem of the plant was always secured (when not stated to the contrary) close to the base of the leaf, the movements of which were being observed, so as to prevent the stem from circumnutating.  As the tracings were made on a vertical glass in front of the plant, it was obviously impossible to trace its course as soon as the leaf became in the evening greatly inclined either upwards or downwards; it must therefore be understood that the broken lines in the diagrams, which represent the evening and nocturnal courses, ought always to be prolonged to a much greater distance, either upwards or downwards, than appears in them.  The conclusions which may be deduced from our observations will be given near the end of this chapter.

In the following list all the genera which include sleeping plants are given, as far as known to us.  The same arrangement is followed as in former cases, and the number of the Family is appended.  This list possesses some interest, as it shows that the habit of [page 320] sleeping is common to some few plants throughout the whole vascular series.  The greater number of the genera in the list have been observed by ourselves with more or less care; but several are given on the authority of others (whose names are appended in the list), and about these we have nothing more to say.  No doubt the list is very imperfect, and several genera might have been added from the ‘Somnus Plantarum’ by Linnaeus; but we could not judge in some of his cases, whether the blades occupied at night a nearly vertical position.  He refers to some plants as sleeping, for instance, Lathyrus odoratus and Vicia faba, in which we could observe no movement deserving to be called sleep, and as no one can doubt the accuracy of Linnaeus, we are left in doubt.