594 
Notes . 
performance of its functions, it seems only likely that others may; 
and consequently, that the study of adaptation must enter upon a new 
phase in connexion with the study of comparative and experimental 
morphology and of variation and correlation. 
Another question raised is the insecurity of our conceptions of 
genera and other taxonomic groups, and the need of some more 
quantitative and phylogenetic basis. We divide the Podostemaceae, 
for example, into genera and sub-orders largely upon the degree of 
dorsiventrality displayed in the flowers and fruits, but we do not know 
the real quantitative or phylogenetic value of the distinctions. It also 
follows from the above conclusion that it is highly probable that many 
genera, species, sub-orders, or even larger groups, may be polyphyletic. 
We can easily imagine a group of allied or similar species, for example, 
all becoming more dorsiventral in their vegetative systems, and at last 
all of them showing the effect in the floral organs. As the effects in 
the latter seem to follow very definite rules, all these species may 
presently form a polyphyletic genus, there being no ancestor which 
has the generic characters. The same reasoning applies to higher 
groups, and in the very largest groups we are already beginning to 
perceive clearly that many, if not most, are more or less polyphyletic. 
It is evident that this view, if it prove true even in part, will help 
in clearing up the darkness which surrounds many of the problems of 
evolution, geographical distribution, &c. 
JOHN C. WILLIS. 
Peradeniya. 
FOLIAR PERIODICITY IN CEYLON 1 .— The high temperature 
and humidity of the air in most parts of Ceylon allow almost continuous 
growth of the arborescent vegetation. There are, however, nearly two 
hundred species which become leafless at different times of the year. 
External and internal factors affect the phenomena of defoliation 
and foliar renewal. The climatic effect is obvious from the fact that 
the majority of our deciduous species become leafless during our 
hottest and driest months. The deciduous trees respond only to one 
hot dry period of three or four months, and not to the dry part of 
each monsoon. Some species undergo complete defoliation twice per 
1 Abstract of paper read before Section K of the British Association, Belfast, 
1903. 
