T H E 
HEW PflYTOIiOGIST. 
Vol. X, No. 3. March, 1911. 
[Published March 31st]. 
FLORAL EVOLUTION ; WITH PARTICULAR REFERENCE 
TO THE SYMPETALOUS DICOTYLEDONS. 
By H. F. Wernham. 
I. INTRODUCTORY. 
I N the following brief review of that group of Angiosperms in 
which a definite corolla, composed of united petals, is present, 
an attempt is made to discover and to display some of the broader 
evolutionary principles or tendencies which underlie floral develop¬ 
ment, as reflected by the various members of that group. 
It will be necessary, at the outset, to discuss in broad general 
outline the purpose and nature of these tendencies ; in other words, 
the initial problem before us is the biological history of the flower. 
The typical flower is an aggregate of sporophylls delimited by 
a perianth ; the perianth, in most cases, determines the individuality 
of the flower. We call a buttercup a single flower because it 
comprises a number of sporophylls associated with a single perianth; 
a daisy, on the other hand, although it consists of a number of 
sporophylls associated with a very definite perianth-like aggregate 
of floral and involucrate leaves, is regarded as an inflorescence, a 
“head” of many flowers, because the sporophyll aggregate is 
capable of sub-division into a number of definite sets or units, each 
associated with a perianth, 
In the attempt to unravel, from the host of floral forms with 
which we have to deal, one or more continuous evolutionary threads 
upon which these forms may be strung in progressively ordered 
arrangement, we need at the outset to fix upon some starting 
point; in other words, we must try to obtain an idea, more or less 
definite, as to what characters are to be regarded as primitive in 
descent, and what as specialized. 
