STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



37 



are themselves this factor, or are very intimately associated therewith. 

 The amino-acids exert this stimulating action on the respiratory 

 activity; they behave very much like a catalyst, accelerating the 

 rate of carbohj^drate catabolism- and resulting in an increased release 

 of energy when the supply of material is decreasing. Thus the 



Si GO 65~ 

 FiGUHE 7. 



Rate of respiration of an entire plant of Helianthus annuus. Soil covered with tinfoil 

 and sealed with cocoa-butter. The ordinate represents rng. COo per hour per gram dry 

 material, and the abscissa the time in hours. 



catabolic activity of the plant tends to be maintained, though the 

 store of fuel is ebbing, until photosynthetic activity again replenishes 

 the fuel supply and the light diminishes the amino-acid content. 

 True to the nature of catalyst, the amino-acids do not yield the 

 energy, but when the concentration of the subsirat (the carbohydrates) 

 is sufficiently decreased, the rate of the general reaction also decreases. 

 This accounts for the dropping in the latter portion of the curve. 



Table 9. 



These respiration curves of necessity show in but a gross manner 

 the course of respiratory activity. They represent the resultant 

 of forces. The reversal of the rate (a drop in the curve) simply 

 indicates when an influence opposed to the stimulatory one is 

 the more potent; it does not show when these various forces 

 started. As the analytical data given in tables 12 and 13 show, 

 leaves attached to the plant draw heavily upon the carbohydrate 



