86 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



been discussed apply to the work on photosynthesis. With a single 

 leaf the illumination in relation to the surface of the leaf can be more 

 accurately controlled than when there is a larger number of leaves. 

 In this way the leaf can at all times be kept at right angles to the 

 source of hght, and the shading by other leaves, or changing of the 

 angle of incidence of the light, can be absolutely avoided. 



The same precautions of culture, cutting, and handling of the 

 leaves which were observed in the work on respiration, already 

 described, apply to the material used for this work. The experience 

 and knowledge gained from a study of the rates of respiration and 

 the changes of material under varying conditions were naturally of 

 great value in a study of the photosynthetic activity. 



N- 





S 



Figure 21. 

 Container for leaf used in photosynthesis experiments. E shows the elevation 

 and a leaf through the glass plates with tube A'^, containing the nutrient solution. 

 <S is the cross section of the container. T is the transverse section showing the 

 glass plates G and the mercury seal. 



A diagram of the apparatus used in these experiments is shown 

 in figure 20. As has been stated, the experiments were carried out 

 in a dark-room which was thermostatically controlled and kept 

 at 20°. The air was taken from a large gasometer. This was first 

 partially filled with carbon dioxid in amounts as required. The 

 carbon dioxid was prepared from white marble and hydrochloric 

 acid and was washed through a solution of sodium carbonate and 



