162 PHOTOSYNTHESIS 



current with photosynthetic inactivity has been observed frequently. ^^^ 

 This is associated vi^ith the aggregation of the chloroplasts into a central 

 clump. In this condition the chlorophyll in the chloroplast is destroyed 

 if illumination is continued. It is interesting that protoplasmic stream- 

 ing, after retardation by light of high intensity, recommences sooner than 

 does the recovery of the original rate of photosynthesis. While the aggre- 

 gation of the chloroplasts probably plays an important role in the inhibi- 

 tion of the photosynthetic activity, it cannot be said that this fact in itself 

 explains the phenomenon. In the fatigue effects observed by Pantanelli 

 the destruction of chlorophyll probably plays no part. But as to the real 

 cause of the temporary inhibition of photosynthesis no definite statement 

 can be made. It is very doubtful that in photosynthesis chlorophyll is 

 successively decomposed and reformed, for Willstatter and Stoll could 

 observe no alteration in the chlorophyll-content during photosynthesis. 

 And when chlorophyll is decomposed, as occurs during very intense illumi- 

 nation, the reforming thereof is a slow process. Therefore it seems at 

 least plausible that in the fatigue effects the colorless portion of the chloro- 

 plasts plays a part. It is doubtful whether we can make much advance 

 in these problems until we know more about the relation of chlorophyll 

 to the colorless portion of the chloroplast. There is, on the one hand, the 

 theory that the chlorophyll and the plasmatic stroma are morphologically 

 separate, and, on the other, that the two are chemically united. In view 

 of the ease with which chlorophyll can be extracted from the plant it is 

 doubtful whether the union of the pigment and the proteinaceous stroma 

 can be of a more stable nature than exists in emulsions. 



An exceedingly important fact in this connection is that photosynthetic 

 activity is apparently intimately associated with the vital activity of the 

 plant. Any disturbance in the respiratory activity of the plant also affects 

 the photosynthetic activity. This is particularly true of narcotics and 

 poisonous substances. Whether the photosynthetic activity is affected by 

 the action of these substances on the protoplasm or on certain enzymes 

 elaborated by the protoplasm is not certain. From the results of Molisch 

 who was able to detect the evolution of oxygen in leaves that had been 

 dried, and the protoplasm consequently killed, it would appear that enzymes 

 play an important role. It may be said that ascribing these functions to 

 an enzyme about which we know virtually nothing, rather than to the 

 protoplasm is just shifting the burden and constitutes no real advance in 

 our knowledge ; it is nevertheless a step in the same direction in which 

 Buchner's discovery of zymase aided in elucidating the phenomenon of 

 fermentation. 



The absence of oxygen also has a profound effect on the rate of photo- 

 synthesis. Boussingault ^^° showed that in an atmosphere of hydrogen, 

 nitrogen or methane plants lose the power of photosynthesis and attributed 



"'Ewart, Ann. Bot., 12, 385 (1898)_; Journ. Linncan Soc, 31, 439 (1896). 

 ™ Boussingault, "Agronomie, chimie agricole et physiologic," Paris, 1868, 4, 

 p. 329. 



