8o 
H. F. Wernham. 
from Cycadeoidea to the Magnoliacese. Heterochlamydy, the 
differentiation of the perianth into a protective calyx and an 
attractive corolla, doubtless went hand in hand with the same 
tendency. 
For the sake of completeness in the tentative formulation of 
these evolutionary principles, it will be necessary at this stage, 
somewhat out of place perhaps, to call attention to a phenomenon 
characteristic of many of the more advanced groups of Archi- 
chlamydeae, namely, indefinite numbers in the androecium. The 
groups concerned are, approximately speaking, comprised in the 
cohorts Centrospermas, Rhaeadales, Parietales, Opuntiales, and 
Myrtiflorse. This indefiniteness is regarded by many, if not 
by all, as primitive, and Celakovsky in his masterly paper, Das 
Reductionsgesetz dev Bluthen, etc ., 1 has described a considerable 
number of types in support of this view. In other respects, 
particularly in the gynaecium, many of these flowers are un¬ 
doubtedly of a relatively advanced type; and if the number of 
stamens be regarded as primitively great, and compared with the 
androecium of the Ranales, we must suppose that the androecium 
has in many cases lagged behind the gynaecium in the course of 
descent. 
This, of course, is by no means an improbable view, but no 
general biological considerations have, to the writer’s knowledge, 
been urged in its support; and a phenomenon so extensive seems 
to call for some explanation. An alternative aspect of the question 
is presented below ; but it must be premised at the outset that the 
aspect is based only upon speculation, and much minute research 
into the structure and development of a host of forms is necessary 
before any hope of a definite decision can be entertained. In any 
case, however, the matter is not one of primary importance for our 
present purpose, which is to furnish an introduction to the study of 
the Sympetalae ; for among these flowers an indefinite androecium 
is an extremely rare feature. 
We have selected the typical Ranalian flower, with indefi¬ 
niteness in the numbers of all its parts, as a starting-point from 
which to trace the working of our principles; we would urge, 
however, that all flowers—such for instance as the Cactus—which 
have a large number of perianth segments, stamens, and carpels, 
are not therefore necessarily primitive. In a large number of cases 
this indefiniteness has resulted from chorisis in descent of the 
1 Site, der Konigl. Bohmischen Ges. der Wiss. Prag. 1895, pp. 1—140. 
