114 Canadian Record of Science. 
where variety and number are reduced to a minimum, and 
life appears to be one continual protest against the condi- 
tions imposed upon it. 
The inquiring mind at once asks what produces this mar- 
vellous charge? ‘To this the answer as naturally comes 
that, with an increased obliquity in the sun’s rays as they 
strike the surface of the earth, there must be corresponding 
variation in the absorption and radiation of heat, and hence 
a lower temperature in the surrounding atmosphere. The 
climate has therefore changed with the progress of our 
traveller, and with it the vegetation of the various latitudes 
through which he has passed. 
We therefore find that botanists are in the habit of 
dividing the surface of the earth into a certain number of 
regions or zones, between the equator and the pole, as de- 
termined by the most characteristic changes in climate and 
vegetation ; and that this offers a somewhat more rational 
and convenient division than that proposed by Grisebach, 
is apparent. Those zones, therefore, with their corres- 
ponding mean temperatures, are as follows :— 
The equatorial zone extending to lat. 15° N. with a mean 
temperature of 26° 30° C. Here the extreme heat, com- 
bined with a high degree of atmospheric humidity, calls 
forth the most luxuriant vegetation, such as impresses the 
reflecting mind in the most profound manner. Palms, 
bananas, rich orchids, luxuriant ferns and gigantic fig trees, 
over and among which swing enormous vines, give a pecu- 
liar character to the region, and bear witness to the highly 
favorable conditions under which organic life has its devel- 
opment. 
The tropical zone, reaching from 15° lat. to the limit 
of the tropics, has a mean temperature of 23°-26° C. Here 
we meet with great variations in temperature. In sum- 
mer, the mercury often exceed 30° C, while in winter 
it sometimes descends below the freezing point. Monsoons 
also constitute one of the characteristic features of the 
climate. Here we also meet with the palms, bananas and 
orchids ; but the tree ferns and fig are the characteristic — 
types. 
