1881. ] by the History of Sex in Plants. 93 
pleteness with which this object is accomplished is of all degrees, 
from Epilobium with its style merely turned to one side, to Iris 
with its short extrorse anthers hidden away under the broad 
styles stigmatic on the inaccessible side; from mere heterostyly 
to complete dichogamy. 
I-need not review the conclusive reasoning by which all these 
morphological modifications are accounted for as the results of the 
long continued agency of insects. It is important only to point 
out that this influence has been powerful enough to reverse the 
entire course of sexual differentiation, which, as we have seen, has 
been in all lower forms constantly in the direction of a more and 
more complete separation of the sexes. It may be said that this 
proves too much, since progress in that advantageous direction 
once gained would not be likely to be lost. The sufficient reply 
to this is that, independently of the natural tendency to revert to 
the normal or monosexual state, when the separative influences 
are withdrawn, the reserve power of possible self-fertilization 
when for any cause cross-fertilization fails,as it clearly often may, — 
is a positive advantage, and one which, under the proper circum- 
stances, natural selection will insure. 
The most significant fact which paleontology reveals is that of 
the simultaneous appearance of an insect fauna and a hermaphro- 
dite flora. When the insects came upon the scene they found 
only a diclinous flora with usually apetalous flowers destitute of 
both fragrance and color. The succeeding strata immediately 
commence to exhibit plants of the rose, mallow, magnolia, pulse, 
and crowfoot families with showy petals, often fragrant, and pro- — 
vided with special nectaries for the secretion of honey. Most of 
these had already made their appearance in the chalk formation, 
while during the Tertiary the still more perfectly organized 
Gamopetalz were developed. The agency of insects in the fertil- 
ization of plants and even in the transformation of flowers to 
adapt them to their uses is no longer questioned by any at all 
familiar with the facts, but wide differences of opinion exist with 
regard to the degree of this influence, and also to the meaning of 
particular facts. Much of this confusion is due to the prevalence 
of the notion to which attention was called at the outset, that all 
adaptation must be regarded as completed at the present time. 
This assumption of a statical condition in nature now, while ad- 
mitting the necessity of a dynamical condition in the past, is 
