42 
The results of these determinations agree in showing that green 
leaves of pineapple plants contain much more peroxidase than chlorotic 
leaves. It is apparent, then, that this chlorosis of pineapples growing 
in calcareous soils is caused by a different disturbance in the plant 
from that in those cases explained by Woods. Woods examaned 
chlorotic leaves from many plants. Some of these yellow leaves had 
been punctured by aphids. The colorless portions of variegated 
leaves, etiolated leaves, tobacco leaves affected with mosaic disease, 
and peach leaves from trees affected with ‘‘yellows”’ and rosette were 
also examined and found to contain more oxidizing enzyms than nor- 
mal green leaves. Although the chlorosis, or lack of chlorophyll, in 
all these cases was attended by an increase in oxidizing enzyms, it is 
evident from the above results with pineapples that the chlorosis of 
leaves is in some cases attended by a diminution of peroxidase. 
In the light of the other work on the pineapple leaves it is probable 
that this deficiency of enzyms in the chlorotic leaves has no bearing 
on the chlorosis, but is merely the result of the degeneration caused 
by the excess of lime and lack of iron in the plant. 
EFFECT OF LIGHT ON THE CHLOROSIS. 
It was observed in the field that plants growing under partial shade 
seemed less chlorotic than those exposed to full sunlight. To see if 
the chlorosis could be much diminished by partial shade a dupli- 
cate of experiment I (see p. 23) was run in a glass house that was 
heavily shaded. 
The plants in the glass house showed very much less chlorosis than 
those exposed in the open. The results of this experiment are incon- 
clusive, however, as the plants in the glass house did not make half the 
growth of those exposed in the open. Since the intensity of the 
chlorosis has been seen to be more or less dependent on the amount of 
growth, the smaller degree of chlorosis in this case was probably due 
to the fact that little growth was made. 
It was found, however, that plants which had become strongly 
chlorotic and which had long ceased to grow, became decidedly 
greener when placed under heavy shade for one or two weeks, but 
when they were again exposed to full sunlight they showed their 
original chlorosis within a few days. 
The explanation of these facts is apparent. It has been shown that 
there is a continuous formation and destruction of chlorophyll in the 
plant.!| The destruction of the chlorophyll is brought about by strong 
sunlight and increases with the intensity of the ight. In the chlorosis 


iH. Euler, Grundlagen und Ergebnisse der Pflanzenchemie, Braunschweig, 1908, pt. 1, p. 193. F. 
Czapek, Biochemie der Pflanzen, Jena, 1905, vol. 1, pp. 452, 453, 468. H. Molisch, Ber. Deut. Bot. Gesell., 
20 (1902), pp. 442-448. Molisch found that aloe leaves that became brown in direct sunlight became green 
again when placed in the shade. f 
[Bull. 11] 


