144 PHOTOSYNTHESIS 



ments. But in this case also, those plants that had a lower rate of photo- 

 synthesis also had a lower rate of respiration. Undoubtedly, however, 

 in these cases questions of light intensity and absorption coefficient enter 

 which make the interpretation of the results very difficult. 



The results of Henrici,'*^ who made a study of the effect of altitude 

 on photosynthesis and chlorophyll-content of the various plants, are also 

 of interest in this relation. The photosynthetic activity and chlorophyll- 

 content was compared of Anthyllis vulneraria, Bcllis perenis, Primula 

 farinosa, and Taraxacum officiuale, grown at different altitudes, the low 

 land material at Basel at 450 m., the alpine material at 1400 to 2700 m. 

 Differences in the structure of leaves, particularly of the chlorophyll 

 bearing portions, with changes in altitude have been observed repeatedly.^*^ 

 Henrici found that the plants grown at high altitudes contain less chloro- 

 phyll than those of the same species from lower altitudes. This is pre- 

 sumably due to the greater intensity of light at higher altitudes. How- 

 ever, whether the lower chlorophyll-content of- plants grown under high 

 illumination intensity can be directly ascribed to the destructive action 

 of such light (especially the red-yellow rays) on chlorophyll, does not 

 seem entirely established.^ '° There is no variation in the chlorophyll-con- 

 tent during the course of the day nor do plants taken from one alti- 

 tude to another change in this respect within two weeks. The photosyn- 

 thetic relations of the plants grown at different altitudes is more complex 

 than would be expected from simply a difference in the chlorophyll-con- 

 tent and is a function of light and temperature. While photosynthesis 

 in the alpine plants (low chlorophyll-content) commences at higher light 

 intensity than the low altitude plants (high chlorophyll-content), the 

 temperature minimum of the former is much lower than the latter. With 

 high light intensity, photosynthesis of the alpine plants is higher than 

 that of the low land plants at any temperature. With low light intensity 

 the photosynthesis of the alpine plants is higher than that of the low land 

 plants only at low temperatures. At higher temperatures, more light 

 is required in order that the photosynthesis of the alpine plants equal 

 that of the low land plants. These results are in agreement with the 

 findings of Willstiitter and Stoll discussed below. The alpine plants can 

 endure a wide range of temperature, and, with their low chlorophyll- 

 content, also high illumination intensities. These plants are apparently 

 well adapted to the conditions of high altitudes, though the conditions 

 of such an adaptation lie not only in a single factor such as the chlorophyll- 

 content, but as well in other factors as the temperature relations of the 

 plants. Henrici's experiments show marked specific differences in the 

 adaptation of the various species of plants used. Her work also serves 

 to demonstrate the great difficulty, if not the impossibility, of obtaining 



^^^ Henrici, Dissertation, Basel, 1918. 

 ""Bonnier, G., Ann. Sci. nat. Bot. (7), 20, 247 (1895). 



^'" Dangerard, P. H., Compt. rend., 151, 1386 (1910). Ewart, Jour. Liinu'an Soc. 

 31, 436 (1896). 



