124 BOOKS AND CURRENT LITERATURE 



variations in carbon dioxide content of the air; method of conducting 

 air to the plants; variations in respiratory activity; use of fresh weight, 

 dry weight, surface or volume of leaves as the proper unit of reference 

 in stating the amount of photosynthate; use of detached leaves or the 

 entire plant as experimental material; character and quantity of light; 

 influence of the plant's content of water and of nutrient salts; influence 

 of leaf exposure and of weather, especially the influence of atmospheric 

 electricity; behavior of stomata during experimentation. 



That different kinds of plants have different effective characteristics 

 might perhaps have been expected, although it is only rarely taken into 

 account. That individuals of the same species behave decidedly dif- 

 ferently when taken from widely different habitats and examined under 

 the same conditions (the author used three experimental stations hav- 

 ing the altitudes given above) is evidenced by the following taken from 

 the author's summary: lowland meadow plants have considerably more 

 chlorophyll than alpine individuals of the same species (often 230% of 

 the latter) ; plants of the snow ravines have exceptionally high chloro- 

 phyll contents (often 350% of the alpine meadow plants) ; cultivation 

 of the alpine meadow plants in lowland stations during several weeks 

 produced no change in chlorophyll content; alpine and lowland plants 

 of four genera reacted specifically toward large changes in character 

 and quantity of light; diurnal variations in chlorophyll content were 

 never found; alpine plants require more light than do lowland plants 

 to assimilate carbon actively, although they do so at much lower temper- 

 atures than the latter; in very strong light alpine plants assimilate more 

 rapidly than lowland plants; in very weak light they assimilate more 

 rapidly than the latter only if the temperature is sufficiently low; each 

 species investigated behaved characteristically in its assimilatory activi- 

 ties; near sunset, when the red rays predominate, alpine plants assimi- 

 late more rapidly than do lowland plants; when blue light predominates 

 the lowland plants are the most active; before storms the alpine plants 

 assimilate more rapidly than lowland plants, indicating a different 

 reactive ability toward atmospheric electricity. 



Some of the results are not in accord with some usually accepted 

 physiological generalizations. It appears that chlorophyll content is 

 more constant when reckoned on fresh weight of leaves than when 

 reckoned on dry weight; amount of photosynthate is more constant 

 when reckoned on leaf volume than on leaf area; high respiratory ac- 

 tivity of individuals is associated with high assimilatory activity; small 

 plants of a species assimilate more rapidly than do large plants; respi- 



