1896.] Vegetable Physiology. 227 



prominent the abundance of anthocyan in many alpine plants as well 

 as the fact that when a species grows on the plains as well as in the 

 mountains it is in the latter locality that the vegetative and floral 

 organs show an inclination to become red with anthocyan. (2) In 

 cases where the cells holding the anthocyan are on the under side of 

 the leaf, the upper side being pure green (Cyclamen europceum, Hydro- 

 charis Morsus ranee) the lightscreen hypothesis naturally falls to the 

 ground. Here there is every reason to believe, according to Kerner, 

 that the light rays which would otherwise pass out of the plant and be 

 lost are converted into heat rays in passing through the cells contain- 

 ing anthocyan. In conformity with this hypothesis we find that the 

 leaves of trees and shrubs which are lifted up from the soil and have 

 other green leaves below to catch the filtered light, are never violet on 

 their under surface, while, in very leafy under shrubs, only the lower- 

 most leaves next the ground are provided with anthocyan. Another 

 indication of the warming influence of anthocyan is its abundance in 

 alpine plants, as already mentioned, and its frequent development in 

 the perennial leaves of other plants during the winter season (Semper- 

 vivtim tectorum, Ligustrum vulgare, Hedera helix. 



the leaves being enabled thereby, in sunny winter days, to break up 

 carbon dioxide even at relatively low temperatures. (3) There are, 

 however, a series of facts going to show that the preceding hypotheses 

 are not sufficient to explain all cases. On full grown shoots of many 

 herbs and woody plants the sunny side of the internodes frequently be- 

 comes red while the opposite side remains nearly or quite pure green 

 (Salix specie-. m, and many other plants). The 



same difference is frequently observed on petioles, the red color being 

 not rarely prolonged into the midrib and its branches. These facts 

 lead to the conclusion that the screen of anthocyan may have some use 

 in connection with the breaking up and translocation of plastic sub- 

 stances through the vascular system. This is also indicated by the fact 

 that when the roots of willows and other plants grow down from a bank 

 into the water and are subject to direct sunlight they become red on 

 the exposed surface. Pick considers the anthocyan screen as a means 

 of bringing about the outward movement of starch in large quantities 

 without seriously disturbing the assimilatory activity of the chloro- 

 phyll bodies. Some effort has been made to demonstrate this third 

 view, but so far as known, no one has tried to establish the first two by 

 means of experiment. The following experiments were, therefore, un- 

 dertaken to fill this gap. (1) Does anthocyan protect chlorophyll from 

 the destructive action of light t Owing to the manifest difficulty of deal- 

 ing directly with the chlorophyll bodies the experiments were made 



