424 G. R. Wieland — Polar Climate in Time. 



or direction other than that based on the proj)erties of matter, 

 including the power of living and undergoing evolution. 



Kerner Yon Marilaun performed various culture experi- 

 ments in tlie powerful light of the Alpine heights of the 

 Tyrol, and his conclusion from tliese is definite. He says :* 



"From these culture experiments two things may be learned : 

 first, that a very brilliant light is able to influence the distribu- 

 tion of plants, and to set up an impassable V)arrier for many of 

 them; secondly, many plants have the capacity of adapting 

 themselves to various degrees of light intensity, but in con- 

 sequence they develop such a varying character that they 

 might be mistaken for wholly distinct species." It also is 

 known that certain species with the foliage exposed to the direct 

 rays of the sun have violet or red hairy leaves, and that these 

 same species growing in shady places may have green and 

 nearly hairless leaves. Again, the leaves of one and the same 

 species may have on low ground few hairs and thin cuticular 

 layers, while on high mountains its leaves may be shrouded in 

 thick grey or white fur and have a thick and leathery texture 

 in consequence of strongly developed cuticular layers. And 

 Kerner further states that herbs with vertically directed leaf 

 surface are never to be met with in shady places. The leaves 

 and branches of plants of vertical habit when brought into the 

 shade tend to twist and bend so as to present a broader leaf 

 surface to the diffuse light. 



It is obvious that in temperate and tropic regions the vertical 

 position of the young and tender leaves of such plants as the 

 ferns and cycads, is a protection against strong sunlight. Later, 

 when thick epidermal layers have formed, the leaf bends into 

 its normal position and catches the nearly full rays of the sun. 

 Curved young pinnules, like those of Cycas^ also afford protec- 

 tion from the hot sun. From such facts, and they could be 

 extensively added to, it is very clear that the peculiar light 

 relations of the Arctic regions must always have had great 

 influence on plant, and perforce on animal life. The further 

 minor changes produced during southward migration could 

 only be deduced from extended careful study. The range 

 of light variation lies between the polar perihelion day or 

 night of 200 solar daj^s, and the equal division of twelve hours 

 of daylight and twelve hours of darkness at the equator. When 

 the greatest local variation in length of light succeeding darkness 

 takes place within the Arctic circle, periods of vernation and 

 reproduction must be more powerfully altered and changed 

 there than elsewhere, reasoning from cause to effect. It would 

 seem also that the liibernation of many animals, including cer- 

 tain forms of such diverse groups as monkeys, bears, and tur- 

 * Page 394 of Oliver's translation of Pflanzenlebeu. 



