122 PROF. T. H. HUXLEY ON THE GENTIANS. 
Gentiana prostrata may have had its present distribution before 
the Glacial epoch. In fact, I am more surprised to find only one 
species widely spread over both the Northern Arctogæal and the 
Austro-Columbian provinces, than I should be if there were 
several; and I am not a little disposed to think that a serious 
critical comparison of the two Flore, with due attention to the 
range of variation of the species in each, may bring about a con- 
siderable alteration of our views on this subject. 
The supposition that the distribution of the Gentianesm in 
Pliocene or in Miocene times was substantially similar to what it 
is now, is of course no solution of the problem of their distribu- 
tion; itis simply driving the search for that solution further 
back Is it possible to fix any anterior limit to this retro- 
gression ? 
I suppose it would be, if one could fix the age of the first ap- 
pearance of Diptera, Hymenoptera, and Lepidoptera provided 
with long haustra. For, upon Müller's hypothesis, the existence 
of the Keratanthe, Stephananthe, Lissanthe, and Ptychanthe 
types presupposes that of such insects. Unfortunately, we are, 
as yet, hardly in a position to speak positively on this point. 
The most that can be-said is that there is no evidence that they 
were abundant before the middle of the Mesozoic epoch, or that 
they existed in Paleozoic times. Free play, therefore, is left to 
speculation ; and I do not think any good grounds could be given 
for denying the existence of even the more specialized Gentiane® 
in the Cretaceous epoch; while the “ Ur-Gentian," the hypothe- 
tical anemophilous Haplanthe, may be dated back almost as much 
further as probabilities permit us to carry the existence of 
flowering plants. For it is obvious that a very slight further 
modification, in the direction of simplicity in Haplanthe, would 
bring about a form of flower which might serve as the starting- 
point for those of almost all the Orders of Dicotyledons. But 
speculation as to when or where the hypothetical Haplanthe 
may have originated is, for the present, idle. '*Ignoramus" and, 
I fear, for a long while, “ ignorabimus." 
Considering how slight the morphological differences between 
the eight types really are, and that (according to the hypothesis) 
they have been brought about by the selective operation of agencies 
of the same order, it seems to me that it would be rash to deny that 
species belonging to the same type may have arisen in different 
