522 SOURCES OF HEAT. TRANSFORMATION OF LIGHT INTO HEAT. 



provided with anthocyanin on both leaf-surfaces. The leaflets and stem of the 

 Alpine Sedum atratum, those of Bartsia alpina, and, above all, numerous species 

 of Pedicularis (e.g. Pedicularis incarnata, rostrata, recutita) are coloured wholly- 

 purple or dark violet, and this in habitats where the colouring could not possibly 

 be regarded as a protection for chlorophyll. It is also a very striking phenomenon 

 that widely-distributed grasses {e.g. Aira ccespitosa, Briza media, Festuca nigres- 

 cens, Miliwm effusum, Poa annua and nemoralis), which in the valley possess 

 pale-green glumes, develop anthocyanin in them on lofty mountains, so that there 

 the spikes and panicles exhibit a deep violet tint, and on this account the regions 

 in which grasses of this kind grow in great quantities receive a peculiar dark 

 colouring. Indeed, this tint becomes the more intense the nearer the habitat 

 of the plants in question is to the snow-line, and the more intense the action of 

 the sunlight becomes. In this case anthocyanin can certainly not be looked upon 

 as a means of protecting chlorophyll, as the glumes generally contain but little 

 of that substance, and take so little part in the formation of organic materials, 

 that the few chlorophyll-grains might be entirely absent without the plant suffer- 

 ing any damage. On the other hand, it may be supposed that the intense light 

 of the elevated region is changed into heat by the abundant anthocyanin of these 

 glumes, that this heat reaches the germs hidden under the glumes, and there 

 favourably influences the growth of the seeds as well as the transformations of 

 materials. The same occurs in the numerous sedges and rushes growing in the 

 Alps, which have dark- violet, almost black, scales covering the flowers (e.g. Carex 

 nigra, atrata, aterrima, Juncus Jacquinii, trijidus, castaneus), and probably 

 some of the varieties of tint observed in the corollas of Alpine plants are also to 

 be explained in the manner indicated. 



It is known that the floral- leaves of many plants growing on lofty mountains, 

 and in the far north, are coloured blue or red by anthocyanin, whilst in the same 

 species, growing in the warm lowlands and in southern districts, they appear white. 

 Particularly noticeable in this respect are the Gypsophyllas (Gypsophylla repens), 

 the Carline Thistle (Carlina acaulis), the large-flowered Bitter-cress (Cardamine 

 amara), the Milfoil {Achillea Millefolium), and many of those Umbelliferae which 

 have a very wide distribution, and occur all the way from the lowlands up to a 

 height of 2500 metres in the Alps, such as; Pimpinella magna, Libanotis montana, 

 Chcerophyllum Gicutaria, and Laserpitium latifolium. Since it has been proved 

 that the colours of flowers are eminently important as a means of attracting 

 insects, it might be thought that the above cases are in some way connected with 

 insect-visits. Without wishing altogether to deny such a relation, the possibility, 

 on the other hand, must not be excluded that anthocyanin plays the same part 

 here in the flowers as in the glumes of grasses, and in the clothing scales of sedges 

 and rushes; and that in the cold Alpine regions, that which is deficient in the 

 amount of heat directly absorbed as such, is compensated for by such as is 

 obtained from light-rays by means of anthocyanin. In support of this view there 

 is also the phenomenon that many plants which develop white flowers in the warm 



