Floral Evolution. in 
regarded as secondary 1 —is a feature of the cohorts Aristolochiales 
and Centrospermae. 
Group ( b ) displays clearly the progressive tendency to oligo- 
mery. The primitively indefinite number of stamens which 
characterizes so many Ranales is comparatively rare in other 
cohorts; we meet it in a few of the Rosales, in the Sarraceniales, 
and possibly in a few of the Rhoeadales; although a dominant note 
in the latter cohort appears to be secondary branching, and the 
indefinite number of stamens found in many Papaveraceae, Cappari- 
daceae, etc., may be secondary, the result of active chorisis. The 
branched stamens in the Fumarieae are suggestive in this connection. 
The arrangement A=C+C, where C denotes the number of 
corolla segments, is attained in a few members of the Ranales, 
Rhoeadales, and Sarraceniales; it prevails in Rosales, Geraniales, 
groups B and D of Sapindales, and in Thymelaeales. 
The condition of isomery, A=C (or less than C in some cases), 
is reached with decreasing rarity as we proceed along the line 
Ranales, Sarraceniales, Rosales, Geraniales, Sapindales (groups 
B, D), and Thymelaeales; it occurs also in some Parietales; it 
prevails in groups C and E of Sapindales, and in Myrtiflorae; and it 
is a constant character of Rhamnales, in which the stamens are 
opposite the corolla-segments, and of Umbelliflorae, where they 
alternate with them. 
The Umbelliflorae may thus be regarded as standing at the head 
of the Archichlamydeae in relation to isomery of the andrcecium, for 
here isomery is a fixed character, and the alternation of the staminal 
whorl with the corolla segments leaves no suggestion of an ancestral 
second whorl. 
The cohorts Rhoeadales, Malvales, Parietales, Myrtiflorae, and 
Opuntiales are here regarded as expressive of the tendency to 
chorisis, of which the Opuntiales are the highest expression. 
Cohesion of stamens, to a greater or less extent, characterizes 
most of the natural orders in Geraniales (groups A, B, C), Malvales, 
and Parietales (group A). 
2. The Gyncecium. In group (a), and in certain so-called 
“ anomalous ” orders, the prevailing number of carpels is 2, e.g .,— 
Verticillatae (Casuarinaceae), Salicales, Myricales, Balanopsidales, 
Juglandales; also Podostemaceae and Callitrichaceae. 
A tendency to reduction appears in Piperales (4 to 1), and 
Urticales (2 to 1); while in Leitneriales, and the highly specialized 
Proteales, a monocarpellary gynaecium is a constant feature. 
Supra , p. 80. 
1 
