1884. 87 Trans. N. Y. Ac. Set. 



Greenland, and thence migrate to low latitudes without change of 

 character, if — to say nothing of temperature — the manner of supplying 

 solar influences was then as different in the two regions as it 

 now is. 



It certainly was to be expected, if plants are to be affected by their 

 surroundings, that natives of high latitudes, adapted to continuous 

 months of sunlight and of darkness, would fail to endure the altered 

 conditions, or else would exhibit indications of changes in structure 

 to correspond to the altered requirements. 



This belief is strengthened by the fact that " in receding from polar 

 toward equatorial latitudes, the Alpine or mountain floras really 

 become less and less Arctic." * The only changed conditions in such 

 cases are those due to the difference in the length of days and nights. 



Another corroboration is afforded by the peculiar structure of a 

 conifer found standing in lat. 72^°, \ and microscopically examined by 

 Sir William Hooker. It differed remarkably frorri all other conifers 

 known to him. Each annual ring consisted of two zones of tissue ; 

 the inner, narrow, of a dark color, and formed of slender woody fibres 

 with few or no discs upon them ; the outer, broader, of a pale color, 

 and consisting of ordinary tubes of wood fibre marked with discs, such as 

 are common to all coniferas. These characters were found in all parts 

 of the wood. They suggest, he says, the annual recurrence of some 

 special cause which modified the first and last made fibres of each 

 year's deposit ; and this cause he thinks is found in the peculiarity of 

 an Arctic climate, where the days were at first very short — a few hours 

 only of sunshine. Then the first and imperfectly developed fibres 

 were formed. As the days grew longer, the solar rays at last became 

 continuous, the woody fibres became more perfect, and were studded 

 with discs of a more highly organized structure than are usual in the 

 natural order to which this tree belongs. 



The absence of such structure in Spitzbergen, 5° further north, if 

 established, would strengthen the conviction that such days did not 

 occur there in the much earlier times, to which its trees belong. 



Since Arctic climate, in those early periods, was warm through the 

 year, it follows that — with the earth's axis inclined 23^°— the plants 

 of Spitzbergen and other equally high latitudes must have spent four 

 months of each year in darkness, and surrounded by a moist and 

 warm atmosphere. Modern vegetation, so placed, bleaches and dies ; 

 could the result then have been different, if the axis was inclined as 

 now ? 



Undoubtedly, a flora might have been specially organized for such 



* Quoted approvingly by Mr. Darwin, in Origin of Species, from Mr. H. C. Watson, 

 t See account in Climate and Time, pages 264 and 265. 



