Notes. 
593 
ON THE DORSIVENTRALITY OF THE PODOSTEMACEAE, 
WITH REFERENCE TO CURRENT VIEWS ON EVOLUTION 
The paper read is an extract from a forthcoming paper in the Annals 
of the Royal Botanic Gardens, Peradeniya, upon the Morphology and 
Ecology of the Podostemaceae. This order shows a very far-reaching 
dorsiventrality of structure, both vegetative and floral. Two lines of 
argument are followed — one morphological, the other ecological. 
Commencing with the less modified types found in the order, which 
show a slight amount of dorsiventrality in the vegetative system and 
none in the floral, a series is traced through the more modified types, 
showing the progressive increase in dorsiventrality of the vegetative 
system followed throughout by an increase in that of the floral, 
showing first in the spathe and bracts, then in the androeceum, next 
in the gynaeceum, and lastly in the interior of the ovary. In the 
next place, the same series, regarded ecologically, shows that though 
the flowers are steadily more and more zygomorphic — a condition 
usually regarded as an adaptation to insect visits and accompanied 
by a horizontal position of the open flower — they at the same time 
stand stiffly erect, and are more and more anemophilous and 
autogamous. 
The most reasonable explanation of these facts seems to be that the 
dorsiventrality of the flowers has been forced upon them, without 
reference to any advantage or disadvantage in the performance of 
their special functions, by the steadily increasing dorsiventrality of the 
vegetative system, the latter being due to the general effect of the total 
conditions of life acting on the hereditary peculiarities of the ancestral 
forms, whether directly or indirectly. Now the dorsiventrality of the 
floral organs is a character of high taxonomic value, and upon the 
various degrees of it the grouping of the Podostemaceae is chiefly 
founded, while it is always regarded as important in other families. 
The conclusion drawn is supported by the facts of dorsiventrality in 
other families, and if admitted as probable opens up a number of new 
points of view, and raises questions which must be settled one way or 
the other. 
If one character of importance may thus be forced upon an organ 
or organs without reference to .any advantage to that organ in the 
1 Abstract of paper read before Section K of the British Association, Belfast, 
1902. 
