, 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.
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