Fig. 125.  Trifolium strictum:  diurnal and nocturnal positions of the two cotyledons and of the first leaf.  I. Seedling viewed obliquely from above, during the day:  Rc, right cotyledon; Lc, left cotyledon; F, first true leaf.  II.  A rather younger seedling, viewed at night:  Rc, right cotyledon raised, but its position not otherwise changed; Lc, left cotyledon raised and laterally twisted; F, first leaf raised and twisted so as to face the left twisted cotyledon.  III.  Same seedling viewed at night from the opposite side.  The back of the first leaf, F, is here shown instead of the front, as in ii.

and the first true leaf (F) projects at right angles to them.  At night (see ii. and iii.) the right cotyledon (Rc) is greatly raised, but is not otherwise changed in position.  The left cotyledon (Lc) is likewise raised, but it is also twisted so that its blade, instead of exactly facing the opposite one, now stands at nearly right angles to it.  This nocturnal twisting movement is effected not by means of the pulvinus, but by the twisting of the whole length of the petiole, as could be seen by the curved line of its upper concave surface.  At the same time the true leaf (F) rises up, so as to stand vertically, or it even passes the vertical and is inclined a little inwards.  It also twists a little, by which means the upper surface of its blade fronts, and almost comes into contact with, the upper surface of the twisted [page 311] left cotyledon.  This seems to be the object gained by these singular movements.  Altogether 20 seedlings were examined on successive nights, and in 19 of them it was the left cotyledon alone which became twisted, with the true leaf always so twisted that its upper surface approached closely and fronted that of the left cotyledon.  In only one instance was the right cotyledon twisted, with the true leaf twisted towards it; but this seedling was in an abnormal condition, as the left cotyledon did not rise up properly at night.  This whole case is remarkable, as with the cotyledons of no other plant have we seen any nocturnal movement except vertically upwards or downwards.  It is the more remarkable, because we shall meet with an analogous case in the leaves of the allied genus Melilotus, in which the terminal leaflet rotates at night so as to present one edge to the zenith and at the same time bends to one side, so that its upper surface comes into contact with that of one of the two now vertical lateral leaflets.]

Concluding Remarks on the Nyctitropic Movements of Cotyledons.—­The sleep of cotyledons (though this is a subject which has been little attended to), seems to be a more common phenomenon than that of leaves.  We observed the position of the cotyledons during the day and night in 153 genera, widely distributed throughout the dicotyledonous series, but otherwise selected almost by hazard; and one or more species in 26 of these genera placed their cotyledons at night