1. The main trend of the Monocotyledonous seedling is
towards precocious development of the plumule,
abortion of the radicle and consequent importance
of an early adventitious root system.
2. The vascular tissue of the cotyledon is disappearing, a phenomenon illustrative of convergent evolution since it occurs in unrelated families. It
may be regarded: -
i. as a progressive tendency, because the plumule
is thereby benefited;
ii. as an indication that the Monocotyledons are
a phylum of decadents, or the residuum of a stock now incapable of change save in the
direction of reduction or curtailment. The
wealth of structural detail revealed in the
seedling is an added argument for this point
3. The habit of the adult may act as a differentiating
factor in three ways -
i. as an aid to the reduction process. The
equipment of the embryo and young seedling
for a geophytic existence in the manner described is doubtless connected with increasing xeromorphy of the adult.
ii. as a check on the reduction process, in order
that organs necessary for the mode of life of
the adult be retained, e.g. a lengthy tap root
in young bulbous plants.
iii, as a direct and forceful cause of reduction in
individuals, e.g. aquatics and epiphytes,
quite apart from its more ancient and widespread effect in directing in an almost imperceptible fashion the evolutionary trend.
4. To the voluminous literature on the origin of
Monocotyledons there is little to add. The single
cotyledon is undergoing reduction; it may be
argued, therefore, that it arose primarily from
the reduction or fusion of two cotyledons. If so,
the assumption that such a union produced a central
type does not account for the anatomy of primitive
seedlings. The sequence revealed by this research
points to the derivation of the phylum from an
ancestor having numerous cotyledonary strands, or
to the alternative of their polyphyletic origin.