THE LEWIS BROOKS MUSEUM. 47 



latitudes suggests a question which has not yet received an 

 answer. These plants required not only far more heat than 

 is now found in polar regions, but they could not survive 

 the present lono; periods of darkness which recur every win- 

 ter. We might, without goiDg counter to the truths of 

 Geology, account for the needed amount of heat. A suffi- 

 cient amount of sunlight, however, cannot be supposed to 

 have existed, unless the axis of the earth has been changed, 

 and such a change is not shown by Astronomy. Principal 

 Dawson suggests that heat alone might suffice to preserve, 

 during the arctic nigbt, plants like those of the Cretaceous. 

 He mentions the fact that Europeans in Greenland can pre- 

 serve hot-house plants by keeping the temperature up to 

 the proper point. But the people in high northern lati- 

 tudes use much light-giving fuel, and we do not know how 

 far the artificial can supply the place of natural light. 

 Besides we do not know how long hot-house plants may be 

 thus preserved, and we cannot compare their growth with 

 that of plants depending on free nature. 



The vegetation of the Tertiary and Quartenary contin- 

 ued to approach in type and distribution that of the pre- 

 sent time. The careful study of the fossil flora of Europe 

 throws a great deal of light upon the history of the plant 

 life of the globe during this period. In Europe the entire 

 character of the vegetation changed several times, and each 

 change brought it nearer to its present character. We find 

 that the formation of zones of climate first indicated in 

 the Cretaceous, continued throughout this later period. The 

 cold of the polar regions increased, and drove towards the 

 equator first all tropical plants, then those requiring a tem- 

 perate climate, and lastly everything except the scanty arc- 

 tic vegetation which we now Hud there. During the same 

 period all the now existing forms gradually took shape and 

 adjusted themselves to the conditions existing at this time. 



We learn from this study of extinct plants that the veg- 



