THE METABOLISM OF PLANTS. 



oxygen by green plants exposed to light, Heinrich found that, 

 in the case of Hottonia palustris, the number of bubbles given 

 off in a unit of time gradually increased as the temperature 

 rose up to 3iC, and that a further rise in the temperature 

 diminished the number of the bubbles evolved until, at 

 56 C, the evolution of gas ceased altogether: 31 C. is 

 then the optimum-temperature for this process in this plant, 

 and 56 C. is the maximum temperature. The optimum- 

 temperature for alcoholic fermentation appears, according to 

 Mayer, to lie between 25 and 30 C. It is not possible to 

 make any general statement as to the optimum-temperature 

 for the action of the various unorganised ferments, for it has 

 been found that the temperature is different for the different 

 kinds of ferments, and for the same kind of ferment obtained 

 from different sources, and that the nature of the liquid in 

 which any given ferment is dissolved affects the position of 

 the optimum-point. Mayer mentions that this point is about 

 50 C. for Emulsin, and for various specimens of Invertin he 

 determined optimum-points between 31 and 48 C. The 

 optimum- and maximum-points for germination have been 

 ascertained by Haberlandt, Sachs, and Just for a number of 

 seeds. 



Haberlandt's determinations are as follows : 



Optimum Maximum 



between between 



Wheat, Rye, Barley, Oat, Flax, Pea 25 31 C. 3 1 37 C. 



Buckwheat 25 31 37 44 



Red Clover, Sunflower, Lucerne 31 37 37 44 



Maize, Hemp, Pumpkin 37 44 44 50 



Melon, Cucumber 31 37 44 50 



Sachs determined the following temperatures : 



Optimum Maximum 



ZeaMais 34-0 C. 46-2 C. 



Phaseolus multiflorus 34-0 46*2 



Cucurbit a Pepo 34*0 46*2 



Wheat 29 - o 42^5 



Barley 29*0 37*5 



Just found the maxima for Wheat and Barley to be 37 38 > 5C. 



