222 
H. F. WernhaM. 
with other considerations. Polypetaly, or an approach to it, occurs 
only in the Oleacese and Salvadoraceae, two groups apparently 
allied together, but isolated, we shall see, from the rest of the cohort. 
GERANIAL STOCK 
RANALIAN STOCK 
Let us consider for a moment the habit of the plants concerned. 
The Oleaceae, Salvadoraceae, Loganiaceae and Apocynacese are for the 
most part arborescent or fruticose; Gentianaceae and Asclepiadaceae 
are mostly herbaceous or suffruticose. The extensive occurrence in 
a group of the herbaceous habit, particularly when combined with 
constancy in numbers in the essential organs, seems to be a more 
or less reliable indication of high evolutionary advance—as witness 
the Composite, the Grasses, the Orchids, and, significant in the 
present connection, the Asclepiads. Such groups, it may be urged, 
owe much of their success in the struggle for existence to their 
modest demands for space, while their slender equipment against 
external severities is compensated by subtleties of structure and 
habit, vegetative and reproductive. 
Indeed, in so far as the herbaceous habit is associated with 
small requirements in the matter of space and the necessity for 
relatively little output of energy to attain maturity, it has a broad 
biological significance, and may be regarded as the expression of a 
definite evolutionary tendency. Not only the Angiosperms, but the 
whole series of vascular plants, provide abundant evidence in support 
of the existence of such a tendency: one need only mention the 
giant Calamarieae and Lycopodiales in comparison with their reduced 
