See pages 3 and 224. To this Division belong the majority of the
Flowering-plants. They are divided into two parallel classes, the
Monocotyledons and the Dicotyledons, which differ from each other not
only in the number of cotyledons, which, with a few exceptions, is one
in the former, two in the latter, but also in the internal structure
of the stem, the venation of the leaves, the number of the parts of
the flower, etc. ~Assuming that these two classes have sprang from a
common origin, it is amongst the Helobieæ in the first, and amongst the
Polycarpicæ in the second class that we might expect to find closely
allied forms, which might reasonably be supposed to have varied less
from this original type. As for the rest, they seem to stand quite
parallel, without exhibiting any close relationship. It is scarcely
proved that the Monocotyledons are the older class.~
[Our knowledge of the forms included under the Angiosperms has
recently been considerably increased by Treub (_Ann. d. Jar. Bot. d.
Buitenzorg_, 1891), who has shown that the Casuarinas differ in many
important points from the typical Angiosperms. Among other characters
the pollen-tube is found to enter the ovule near the chalaza and
therefore at the opposite end to the micropyle, and Treub therefore
suggests that these plants should be placed in a subdivision termed
Chalazogams.
According to this view the principal divisions of the Angiosperms would
be represented thus:--
=Angiospermæ.=
Sub-division. Sub-division.
CHALAZOGAMES. POROGAMES.
Class. Classes.
Chalazogames. Monocotyledones, Dicotyledones.
More recently Nawaschin (_Bull. Acad. Imp. Sci. St. Petersb._, ser.
iii., xxxv.) has shown that _Betula_, and Miss Benson (_Trans. Linn.
Soc._, 1894) that _Alnus_, _Corylus_, and _Carpinus_ also belong to the
Chalazogams.
Our knowledge, however, is still so incomplete that one would hesitate
to accord the full systematic value which Dr. Treub attaches to his
discovery until the limits of the Chalazogamic group are better
defined; and it would hardly be justifiable to include the Casuarinas
and the above-noted genera in one family.]