376 
H. F. Wernliam. 
ancestors. For it is in this group that the Economy Principle is 
but little advanced upon the stage generally characteristic of 
Archichlamydeae, in which the androecium consists typically of two 
or more whorls. As we have seen in Chapter 111, the working of 
the Economy Principle, reflected in Pentacyclidae, bridges the gulf 
between Archichlamydeae and Sympetalae. At least 80 polypetalous 
species are included in Ericales— Pyrola, Clethra, Ledum, Monotropa, 
etc. Of Primulales, Myrsinaceae have over 60 species with poly¬ 
petalous flowers (e.g., Embelia) ; Primulaceae include only a few 
such, viz., Apochoris and some species of Asterolinum ; in 
Plumhaginacee the majority of the species have flowers with 
petals quite free or barely united at the base (e.g., Acantholimon, 
Stcitice, Armeria). The same applies to Styracaceae, notably to 
Styrax, with over 60 species, and to Symplocaceae, with over 150 
species. 
Turning now to Tetracyclidae: in the flowers of the oleaceous 
Linociera, Forestiera, and Fraxinus, the petals are at most but 
slightly coherent at the base, and are often quite free ; over 20% of 
the Oleaceae have flowers with free or sub-free petals. In the 
allied Salvadoraceae, with scarcely a dozen species, polypetaly is 
the rule rather than the exception. Beyond these examples 
polypetaly is extremely rare in Tetracyclidae, being confined almost 
exclusively to less than a score of species of Campanulaceae ( Cyphia, 
Nemacladns, Dialypetal urn). Indeed, in the case of this last-named 
family, in which splitting of the corolla-tube is a common feature 
(e.g., Lobelia), it is questionable whether the dialypetalous condition 
is invariably primitive ; and the same question may apply to others 
among these excepta. 
In our preliminary examination of the history of floral evolution 
(Chapters I and II), we were led to elucidate two main biological 
principles of advance, namely, the Economy Tendency, and the 
compensatory Tendency to Adaptation for the reception of Insect- 
visitors. The reflection of the working and mutual interaction of 
these two principles as seen in a general review of the various 
floral forms goes far to support the idea of progressive continuity 
of the two series of Dicotyledons ; for had the Sympetalae as a 
whole been separately evolved from Proangiosperms, we should 
expect not unreasonably to find all stages of the working of the 
Economy Principle reflected as extensively among sympetalous as 
among polypetalous forms. This, as we have seen already in 
Chapter II, we do not find; for quite 80% of the Sympetalae have 
