136 Sargant . — The Reconstruction of a Race of 
the possession of that member to be a character which isolates them from 
other groups will depend largely on the views he holds on the primitive 
form of flower. 
The subject has been so fully discussed in Messrs. Arber and Parkin’s 
recent paper (4) that I will not treat it at length here. The difficulty arises 
from the astonishing variety in the floral structure of the Angiosperms. 
No botanist has yet succeeded in framing a definition of a flower which 
will include every form among them and yet exclude the reproductive 
organs of all Gymnosperms and Pteridophytes. The presence of a carpel 
indeed separates hermaphrodite and female flowers in Angiosperms from 
the corresponding organs of Gymnosperms and other groups, but male 
Angiospermous flowers have also to be distinguished from the male cones 
of other plants. Nor does a definition depending on the presence of a 
carpel add any weight to the collective argument in favour of a mono- 
phyletic origin, since we have already considered that character separately. 
Yet in practice it has been found the most convenient plan to confine 
the term c flower ’ to the Angiosperms. Gymnosperms were long ranked 
among Flowering Plants, but the difficulty of describing their reproductive 
axes in floral terminology has produced quite a literature on the homologies 
of the Gymnospermous cone and its parts. This difficulty suggests that 
there is something unique about the flower of the Angiosperm. What then 
are its differentiating characters ? 
The complete flower with its concentric whorls of perianth-leaves, 
stamens, carpels, really is confined to the Angiosperms. Those botanists 
who maintain that all other floral forms are modifications of this type, 
reduced from it, are justified in declaring that a true flower is not found 
outside the group. On this view all Angiosperms display traces of a 
complete flower, and the presumption that it was inherited from a common 
ancestor is then very strong. The antiquity of the complete flower as 
compared with the simple unisexual type is very strongly supported by 
Messrs. Arber and Parkin. The subject will be better discussed when 
we attempt the reconstruction of the Primitive Angiosperm. For the 
present it is sufficient to say that I agree with this view, and the possession 
of a true flower is therefore in my opinion a further argument for the 
monophyletic origin of Angiosperms. But the case in favour of such an 
origin is already so strong that it is not necessary to insist on corroborative 
evidence. 
Reconstruction of the Primitive Angiosperms. 
In the previous section I have given reasons for believing that Mono- 
cotyledons and Dicotyledons are derived from a single stock which was 
Angiospermous in all its essential features. This race of plants may be 
called for convenience the Primitive Angiosperms. The term must be 
