FROM THE STANDPOINT OF AN IDEALIST. 453 
diversification of conditions, and all we have to look for is the assertion of 
man’s predominance in his replacement of natural floras by his cultivated 
plants and his weeds. The time for revolutions in the plant-world was 
spent geological ages ago ; and Nature in her present operations can offer 
us but little aid in unravelling the revolutionary past. 
The subject of the detachment of the temperate from the tropical floras 
during the ages through which the differentiating influences have reigned 
supreme, brings up the question of the complemental families, those which, 
although now ranked as distinct families in the tropical and temperate 
zones, are so closely linked together that they may be regarded as the result 
of the differentiation of the same world-ranging family-type. Thus we may 
view the Primulaces in the temperate regions and the Myrsinaces in the 
tropics as complemental to each other and as representing the first step 
in the differentiation of a common parent type. In the same way and 
with the same implications we may link the Umbelliferae (temperate) with 
the Araliacee (tropical), and the Chenopodiaces (temperate) with the 
Amarantacez (tropical). 
But the effect of the secular differentiation of climatic conditions and 
of the individualization of the temperate zones has not always been the 
development of a world-ranging type into separate tropical and temperate 
families. Some, like the Composite, have, as far as the retention of family 
characters is concerned, defied the differentiating agencies. In yielding to 
the exigencies of the differentiation of climates, though still holding the 
world, they have retained in this case the essential characters of the family, 
on the absolute permanence of which, in the case of the Composite, Bentham 
lays stress. Others like the Scitaminez are still confined to their original 
home in the equatorial regions of the globe, having failed to adapt themselves 
to the newly differentiated temperate zones. ‘They have given rise to 
separate sub-families, often ranked as families, in the different warm regions 
of the globe, but in no sense as the result of the secular diversification of 
climate. 
We have remarked that the work of the differentiation of floras is largely 
spent, as far as climatic influences are concerned. Yet, great as this work 
has been, we are, as the writer thinks, not justified in regarding it from any 
other standpoint than that of adaptivity. It is not the work that was 
carried on in those remote Mesozoic ages when the larger plant-groups, now 
represented by the alliances of families and by the cosmopolitan and pan- 
tropical families, were first developed. The charaeters that distinguished 
them then distinguish them now, and as far as their essential characters are 
concerned they have made but little response to the great climatic differen- 
tiation of the ages. The rise of the Xerophytes presents one of the most 
important and far-reaching results in the story of distribution and differen- 
tiation, Yet they are of the later and not of the earlier age; and it is 
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