vi COLOURS OF PLANTS 407 



long summer days. " The farther we advance towards the 

 north the more the leaves of plants increase in size, as if to 

 absorb a greater proportion of the solar rays. M. Grisebach 

 says that during a journey in Norway he observed that the 

 majority of deciduous trees had already, at the 60th degree 

 of latitude, larger leaves than in Germany, while M. Ch. 

 Martins has made a similar observation as regards the legu- 

 minous plants, cultivated in Lapland." 1 The same writer goes 

 on to say that all the seeds of cultivated plants acquire a 

 deeper colour the farther north they are grown, white hari- 

 cots becoming brown or black, and white wheat becoming 

 brown, while the green colour of all vegetation becomes more 

 intense. The flowers also are similarly changed : those which 

 are white or yellow in central Europe becoming red or orange 

 in Norway. This is what occurs in the Alpine flora, and the 

 cause is said to be the same in both the greater intensity of 

 the sunlight. In the one the light is more persistent, in the 

 other more intense because it traverses a thinner atmosphere. 

 Admitting the facts as above stated to be in themselves 

 correct, they do not by any means establish the theory 

 founded on them ; and it is curious that Grisebach, who has 

 been quoted by this writer for the fact of the increased size 

 of the foliage, gives a totally different explanation of the 

 more vivid .colours of arctic flowers. He says : " We see 

 flowers become larger and more richly coloured in proportion 

 as, by the increasing length of winter, insects become rarer, 

 and their co-operation in the act of fecundation is exposed to 

 more uncertain chances" (Vegetation du Globe, vol. i. p. 61 

 French translation). This is the theory here adopted to 

 explain the colours of Alpine plants, and we believe there are 

 many facts that will show it to be the preferable one. The 

 statement that the white and yellow flowers of temperate 

 Europe become red or golden in the arctic regions must, we 

 think, be incorrect. By roughly tabulating the colours of 

 the plants given by Sir Joseph Hooker 2 as permanently 

 arctic, we find among fifty species with more or less con- 

 spicuous flowers, twenty -five white, twelve yellow, eight 



1 Revue des Deux Mondes, 1877" La Vegetation dans les hautes Lati- 

 tudes," par M. Tisserand. 



2 "On the Distribution of Arctic Plants," Linn. Trans, vol. xxiii. (1862). 



