1894.) . The Meaning of Tree-Life. 575 
that there were regions of glacial cold in previous, as well as 
several subsequent, ages is highly probable; but this does not 
invalidate the general principle suggested here. The recon- 
structive meteorology of the near future will probably demon- 
strate that the geographical distribution ot the Carboniferous 
glaciation, and of several other similar cases, is directly con- 
nected with peculiar stages of continental evolution and 
oceanic extension. And while such glaciations are of far- 
reaching importance for their age, they are nevertheless 
temporary “ perturbations ” that do not, in the long range of 
time, break down the secular increase in the direct subordi- 
nating of the zonal world-climate to astronomical, rather than 
terrestrial, influences. From a nearly homogeneous climatic 
condition throughout the world, there were gradually 
developed five fairly distinct zones merging into each other 
at their adjacent margins—a torrid equatorial, frigid polar, 
and temperate intermediate. Their development inevitably 
had a profound effect on vegetation. In the fossil forest 
beds of Cretaceous times in far northern regions, there have 
been found side by side Cycads, Conifers, Palms and Hard- 
wood trees, a conglomeration utterly bewildering to the botan- 
ist of to-day, but nevertheless a typical indication of the rela- 
tively homogeneous climatic conditions of the age when such 
a forest could have existed. 
With such a suggestion of the Mesozoic world before us, let 
us watch the great climatic zones develop. It is the tree-life 
of the forests that tells the story most clearly; to it belonged 
preeminently the all-important mission of remodeling the 
aspect of the world’s vegetation. The trees moved their hab- 
itats, and the herbaceous forms were carried along with them. 
In the equatorial belt were all the conditions of heat and 
moisture most favorable to the vigorous development of plant 
life; in the polar regions that sternest foe, steadily increasing 
cold; in the temperate belts, à compromise between the con- 
ditions of the others. From the original mixed forest a 
selection had to be made of the tree-groups that were to 
hold dominion respectively over each of the new sets of con- 
ditions. How? It will not do to say glibly, the Palms 
