180 LIVING PLANTS 



of carbohydrates and other substances from 

 one part of the plant to another, notably 

 starch, from theleaves to the stem. The third 

 theory consists of the idea that the heat de- 

 veloped by anthocyan serves chiefly as an aid 

 in promoting transpiration. Many facts are 

 at hand supporting both the first and last 

 named speculations, though the argument in 

 either case has not advanced to the stage of 

 absolute proof. As for the second, many 

 plants growing in cold situations are un- 

 doubtedly able to carry on metaboHsmto bet- 

 ter advantage because of the heat derived 

 from light by layers of anthocyan present. 



The ''screen'' theory receives support from 

 the fact that the upper layers of leaves of 

 plants growing in intense sunlight and in ex- 

 posed Alpine situations are furnished with 

 layers of color on the upper or illuminated 

 surfaces of the leaves, as are also the leaves 

 of many shade-loving plants when grown in 

 free sunlight. It is likewise asserted that 

 plants devoid of color growing in the low- 

 lands will develop anthoc^^an in the leaves 

 when transplanted to Alpine elevations. Ker- 

 ner transplanted the summer savory (Satur- 

 eja hortensis) from lowland to a height of 

 3,200 meters and found that it developed a 

 very strong layer of anthocyan. Ewart found 

 that the plants on the summit of the moun- 



