1890.] The Distribution of Plants. 829 
species, particularly from regions still imperfectly known botani- 
cally, into the great herbaria where proper facilities for study and - 
clasification are provided. 
There is great need of more exact observations of actual cases 
of transportation of seeds to great distances. "We are not yet in 
a position to say, with definiteness, how much can be explained in 
this way. Whoever records a single absolutely reliable observa- 
tion of this kind will render a good service. 
Climatic changes remain, and probably must still remain, the 
the least definite of all the factors thus far considered. From 
whatever source it may come, a clearer conception of the physical 
conditions formerly prevailing in the Southern hemisphere seems 
indispensable. This is, perhaps, not hopeless, but it is, to all 
appearances, not likely to be immediately realized. 
Paleontological evidence has been slowly accumulated, enough 
to show how much need there is of more. Species now perfectly 
isolated, living in tropical America on the one hand, and in 
Southern Asia on the other, have had their relations cleared up 
by finding their ancestral forms scattered through the intervening 
regions; and the prosecution of this part of the study is as hope- 
ful as it is difficult. But the successors of Heerand Lesquereux 
are not likely to be numerous, nor to turn out results very rapidly. 
One more side of approach remains, seemingly most hopeful, 
perhaps really most hopeless of all; offering almost unlimited 
possibilities, but involving endless labor and endless complica- 
tions. This is the study of single groups from a more strictly 
biological standpoint. Nothing but the merest beginning has 
yet been made. The method is illustrated in a short paper re- 
cently prepared by Prof. Huxley ; more, apparently, as a piece of 
tentative preliminary work suggestive of what may be done than 
as a formal contribution.' 
Spending a few weeks, in the summer of '86, in the mountain 
region near the valley of the Rhone, he began to study some of 
Alpine flowers, and among them the gentians. He at once ex- 
perienced trouble in *analyzing" the species, which, as in so 
many other cases, obstinately refused to conform to the book 
16 Jour. Linn. Soc., Vol. XXIV., 1888. 
