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vi COLOURS OF PLANTS 407long summer days." The farther we advance towards thenorth the more the leaves of plants increase in size, as if toabsorb a greater proportion of the solar rays. M. Grisebachsays that during a journey in Norway he observed that themajority of deciduous trees had already, at the 60th degreeof latitude, larger leaves than in Germany, while M. Ch.Martins has made a similar observation as regards the leguminousplants, cultivated in Lapland." 1 The same writer goeson to say that all the seeds of cultivated plants acquire adeeper colour the farther north they are grown, white haricotsbecoming brown or black, and white wheat becomingbrown, while the green colour of all vegetation becomes moreintense. The flowers also are similarly changed: those whichare white or yellow in central Europe becoming red or orangein Norway. This is what occurs in the Alpine flora, and thecause is said to be the same in both the greater intensity ofthe sunlight. In the one the light is more persistent, in theother more intense because it traverses a thinner atmosphere.Admitting the facts as above stated to be in themselvescorrect, they do not by any means establish the theoryfounded on them ;and it is curious that Grisebach, who hasbeen quoted by this writer for the fact of the increased sizeof the foliage, gives a totally different explanation of themore vivid .colours of arctic flowers. He "says: We seeflowers become larger and more richly coloured in proportionas, by the increasing length of winter, insects become rarer,and their co-operation in the act of fecundation isexposed tomore uncertain chances" (Vegetation du Globe, vol. i.p. 61French translation). This is the theory here adopted toexplain the colours of Alpine plants, and we believe there aremany facts that will show it to be the preferable one. Thestatement that the white and yellow flowers of temperateEurope become red or golden in the arctic regions must, wethink, be incorrect. By roughly tabulating the colours ofthe plants given by Sir Joseph Hooker 2 as permanentlyarctic, we find among fifty species with more or less conspicuousflowers, twenty -five white, twelve yellow, eight1Revue des Deux Mondes, 1877" La Vegetation dans les hautes Latitudes,"par M. Tisserand.2"On the Distribution of Arctic Plants," Linn. Trans, vol. xxiii. (1862).