218 EVOLUTION OF PLANTS 
In passing from the lower to the higher types there 
is a reduction in the number of parts, accompanied by 
their cohesion. The carpels are first affected, and then 
the sepals, and finally the corolla. Reduction in the 
number of stamens is common in certain groups, espe- 
cially the Labiatifloree, and the cohesion of the stamens 
among themselves occurs regularly in the Composite, but 
is much less perfect than that of the other floral parts. 
Most of the more specialized types, both of Choripetale 
and Sympetale, have inferior ovaries. 
The Sympetale are unquestionably the highest of the 
Angiosperms. Whether the group is a homogeneous 
one, or, as seems more likely, sympetaly has originated 
more than once, must be determined by further re- 
searches. The radially symmetrical (actinomorphic) 
Isocarpz are probably nearer the Choripetale, as shown 
by the occurrence of forms like Monotropa, which have 
sepals and petals quite distinct. It has recently been 
suggested that the Isocarpe have perhaps been derived 
from the Centrosperme among Choripetalze and have 
given rise to the Tubiflore and Labiatiflore, whose 
highest members are the mints and figworts. Another 
line, originating from the Calyciflore, has through the 
Umbelliferee developed the Rubiacez (madder family), 
and through these the Composite. There are several 
less important lines of development which cannot be 
taken up here, and it must be remembered that the 
suggestions given here as to the origin of the different 
groups of Dicotyledons are likely to be essentially 
modified when we are in possession of data more com- 
plete than we now possess. The accompanying diagram 
illustrates graphically the arrangement of the principal 
groups of Dicotyledons adopted here. 
