PREFACE 



IT was affirmed a few years ago, by one of the most eminent 

 of living biologists, that it "is no time to discuss the origin 

 of the Mollusca or of Dicotyledons, while we are not even sure 

 how it came to pass that Primula obconica has in twenty-five 

 years produced its abundant new forms almost under our eyes.'* 

 To this statement I venture to demur. I yield to none in my 

 admiration for the results achieved by the analytical methods 

 introduced by Mendel, and I do not doubt the possibility that 

 the direct experimental study of variations and their inheritance 

 may eventually play a large part in bringing the tangled 

 problems of evolution into the full daylight for which we all 

 hope. But this is no reason for condemning those countless 

 uncharted routes which may lead, even if circuitously, to the 

 same goal. Any step towards the solution of the essentially 

 historical problems of Botany for example those concerned 

 with the origin and development of such morphological groups 

 as the Dicotyledons, or of such biological groups as the Aquatic 

 Angiosperms must necessarily contribute some mite to our 

 conceptions of the course of evolution. These less direct 

 methods of approaching the central problem of biology may 

 perhaps, at the best, bring only a faint illumination to bear 

 upon it, but in the deep obscurity involving all evolutionary 

 thought at the present time, we cannot afford to despise the 

 feeblest rush-light; even the glimmering of a glow-worm may 

 at least enable us to read the compass, and learn in which 

 direction to expect the dawn. 



I approached the study of Water Plants with the hope that 

 the consideration of this limited group might impart some 

 degree of precision to my own misty ideas of evolutionary 

 processes. Botanists seem to be universally agreed that the 



