272 PHYSIOLOGY OF NUTRITIOX. 



described above. Further information may also be obtained from 

 the cited work of Aereboe. The utmost attention must be directed 

 to keeping the research material constantly exposed to the same 

 temperature during the alternate periods of light and darkness 

 (the shading can be readily effected by covering the water-box 

 with a suitable cardboard box, open below). Using the alum 

 solution, this is possible, as I know from experience, even when 

 working with direct sunlight. The experiments teach that 

 light rays exert a photo-chemical action on respiration, probably 

 in a very few cases only. Very generally, chlorophyll-free plants 

 respire the same quantity of Carbon dioxide in the light as in the 

 dark. 



Indirectly, of course, the light exerts an important influence on 

 the respiration of plants, because, through its instrumentality, 

 substances are produced as a result of assimilation which in 

 respiration undergo oxidation. To prove this we germinate seed- 

 lings of Lupinus in the light in flower-pots. When the plants 

 are a few weeks old, we select twenty -five very uniformly de- 

 veloped specimens, cut the sterns immediately above ground, and 

 determine the quantity of Carbon dioxide which they produce in 

 two hours at a temperature of 20 C. The flower-pots are now 

 put in the dark, and after two or three days we again investigate 

 the respiration of twenty-five plants. The plants in the flower- 

 pots are then normally illuminated once more, and after four days 

 twenty-five examples are again examined. A series of experi- 

 ments, conducted by Aereboe under my direction, yielded the 

 following results : The twenty-five plants produced in two hours 

 at a temperature of 20 C. : 



Aug. 6, evening, 18'35 mgr. C 2 (after illumination) ; 



Aug. 9, evening, 7'95 mgr. (after being shaded for 2} 



days) ; 



Aug. ]3, evening, 18*72 mgr. ,, (after being illuminated from 



Aug. 9 to Aug. 13) . 



The arrangement indicated in Fig. 101 may suitably be employed 

 for researches on the normal respiration of roots, when it is 

 required to determine the quantity of Carbon dioxide produced in 

 organs vegetating normally, and still remaining in attachment 

 with the aerial parts of the plants. A large glass cylinder placed 

 in a water tank is used for the culture vessel, and contains a food 

 solution. The halved cork employed to close the cylinder may 

 be pushed in till the top of it is about 3 cm. below the rim of 



