Dicotyledons and Monocotyledons distinguished alike in vegetative
and in reproductive construction, yet showing remarkable parallel
sequences in development; and we see that the Dicotyledons are the
more advanced and show the greater capacity for further progressive
evolution. But there is no sound basis for the assumption that
the Dicotyledons are derived from Monocotyledons; indeed, the
palaeontological evidence seems to point to the Dicotyledons being
the older. This, however, does not entitle us to assume the origin
of Monocotyledons from Dicotyledons, although there is manifestly a
temptation to connect helobic forms of the former with ranal ones of
the latter. There is no doubt that the phylum of Angiosperms has not
sprung from that of Gymnosperms.

Within each class the flower-characters as the essential feature
of Angiosperms supply the clue to phylogeny, but the uncertainty
regarding the construction of the primitive angiospermous flower gives
a fundamental point of divergence in attempts to construct progressive
sequences of the families. Simplicity of flower-structure has appeared
to some to be always primitive, whilst by others it has been taken to
be always derived. There is, however, abundant evidence that it may
have the one or the other character in different cases. Apart from
this, botanists are generally agreed that the concrescence of parts of
the flower-whorls--in the gynaeceum as the seed-covering, and in the
corolla as the seat of attraction, more than in the androecium and the
calyx--is an indication of advance, as is also the concrescence
that gives the condition of epigyny. Dorsiventrality is also clearly
derived from radial construction, and anatropy of the ovule has
followed atropy. We should expect the albuminous state of the seed
to be an antecedent one to the exalbuminous condition, and the recent
discoveries in fertilization tend to confirm this view. Amongst