TUA MEN o: HE 
FROM THE STANDPOINT OF AN IDEALIST. 451 
the Angiosperms, commencing with the Monocotyledons and ending with 
the Sympetale, take no heed of the present distribution of land and water. 
But there is a slight response for the cohorts, 9 per cent. of them being 
restricted to either the New or the Old World. Of the families 30 per 
cent., of the tribes about 44 per cent., of the genera at least 80 per cent., 
and of the species about 99 per cent. respond to the cleavage of the land 
into two main masses diverging from the north polar regions (Table I.). 
This contrast in the behaviour of the larger and lesser plant-groups implies 
a very great contrast in geographical and climatic conditions. There would 
seem to have been a pre-differentiation era that corresponded with geo- 
graphical and climatic conditions very different from those that now prevail. 
At that time generalized types ranged the globe and the conditions were 
far more uniform than at present. It was an age, we imagine, when floral 
mutations were relatively unchecked. After that era the age of differen- 
tiating conditions began, the effect of the progressive differentiation of 
conditions being to restriet more and more the play of mutation in the case 
of the floral organs, so that in our age the capacity is rarely exercised. In 
the pre-differentiation era the generalized type had the whole earth for its 
range and uniformity of conditions for its “ mise-en-scène,” a setting that 
was destroyed when climate began to individualize. During such an era 
reigned other things, other ways, and other conditions. 
If we were to draw a line dividing this distant era from the succeeding 
ages of differentiation, we should draw it just below the great family groups 
as illustrated by the Compositze and the Araceze ; and if we were to contrast 
the geographical conditions, we should point to the fact that whilst the 
family and the groups behind it or above it mainly or entirely ignore 
_the existing arrangement of land and sea, the genus and the species are in a 
sense the offspring of it. Distribution in the distant past was chiefly a story 
of generalized family types. In the later ages it has been principally a 
story of the genus and the species and of adaptive response to the progressive 
differentiation of conditions. The failure of the larger plant-groups to 
respond to the great bi-cleavage of the land-mass and their subsequent 
ready response to climatic differentiation mark out the two great eras—the 
pre-differentiation age and the age of differentiation that followed. 
What is earliest in distribution belongs to the family and the large groups 
behind it. What is recent belongs to the genus and the species. To employ 
the terms “ genus” and “species” when speaking of an age different in 
almost every respect from the present one is to muddy the waters, or, 
rather, to confuse the issues. Such a habit assumes that the present is like 
the past, that we can picture what has been from what is. Yet to think 
only in terms of genera and species is to ignore the better half of the story 
of the development of the plant-world. The age that witnessed the rise of 
