pudica, in which
the third leaf above the cotyledons bore only two pinnae, each with only 3
or 4 pairs of leaflets, of which the inner basal one was less than half as
long as its fellow; so that the whole leaf resembled pretty closely that of
M. albida. In this latter species the main petiole terminates in a little
point, and on each side of this there is a pair of minute, flattened,
lancet-shaped projections, hairy on their margins, which drop off and
disappear soon after the leaf is fully developed. There can hardly be a
doubt that these little projections are the last and fugacious
representatives of an additional pair of leaflets to each pinna; for the
outer one is twice as broad as the inner one, and a little longer, viz.
7/100 of an inch, whilst the inner one is only 5/100 - 6/100 long. Now if
the basal pair of leaflets of the existing leaves were to become
rudimentary, we should expect that the rudiments would still exhibit some
trace of their present great inequality of size. The conclusion that the
pinnae of the parent-form of M. albida possessed at least three pairs of
leaflets, instead of, as at present, only two, is supported by the
structure of the first true leaf; for this consists of a simple petiole,
often bearing three pairs of leaflets.
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