the gorse, or Ulex, is not narrow and spinose like the older leaves.  On the other hand, with many Leguminous plants, for instance, Cassia, Acacia lophantha, etc., the first leaf has essentially the same character as the older leaves, excepting that it bears fewer leaflets.  In Trifolium the first leaf generally bears only a single leaflet instead of three, and this differs somewhat in shape from the corresponding leaflet on the older leaves.  Now, with Trifolium Pannonicum the first true leaf on some seedlings was unifoliate, and on others completely trifoliate; and between these two extreme states there were all sorts of gradations, some seedlings bearing a single leaflet more or less deeply notched on one or both sides, and some bearing a single additional and perfect lateral leaflet.  Here, then, we have the rare opportunity of seeing a structure proper to a more advanced age, in the act of gradually encroaching on and replacing an earlier or embryological condition.

The genus Melilotus is closely allied to Trifolium, and the first leaf bears only a single leaflet, which at night rotates on its axis so as to present one lateral edge to the zenith.  Hence it sleeps like the terminal leaflet of a mature plant, as was observed in 15 species, and wholly unlike the corresponding leaflet of Trifolium, which simply bends upwards.  It is therefore a curious fact that in one of these 15 species, viz., M. Taurica (and in a lesser degree in two others), leaves arising from young shoots, produced on plants which had been cut down and kept in pots during the winter in the green-house, slept like the leaves of a Trifolium, whilst the leaves on the fully-grown branches on these same plants afterwards slept normally like those of a Melilotus.  If young shoots rising from the ground may be considered as new individuals, partaking to a certain extent of the nature of seedlings, then the peculiar manner in which their leaves slept may be considered [page 416] as an embryological habit, probably the result of Melilotus being descended from some form which slept like a Trifolium.  This view is partially supported by the leaves on old and young branches of another species, M. Messanensis (not included in the above 15 species), always sleeping like those of a Trifolium.

The first true leaf of Mimosa albida consists of a simple petiole, often bearing three pairs of leaflets, all of which are of nearly equal size and of the same shape:  the second leaf differs widely from the first, and resembles that on a mature plant (see Fig. 159, p. 379), for it consists of two pinnae, each of which bears two pairs of leaflets, of which the inner basal one is very small.  But at the base of each pinna there is a pair of minute points, evidently rudiments of leaflets, for they are of unequal sizes, like the two succeeding leaflets.  These rudiments are in one sense embryological, for they exist only during the youth of the leaf, falling off and disappearing as soon as it is fully grown.