8 i8 Irving.—Photosynthesis and Chlorophyll ’. 
In many of these experiments with cut shoots the development of 
chlorophyll is very slow. This is no doubt to be attributed to the lack of 
carbohydrate reserves in these growing shoots, as Palladin 1 has shown that 
the rate of greening of etiolated shoots is closely correlated with the presence 
of sugar. 
There seems to be no reason to regard this slow greening as detrimental 
to the validity of the conclusions drawn here. 
Conclusion. 
It is clearly established by the foregoing experiments that etiolated 
leaves do not possess any appreciable power of carrying out photosynthesis 
of C 0 2 , either when they are orange yellow, or when they have developed 
a large part of their green chlorophyll. 
It is possible that there may be present a minute potentiality of photo¬ 
synthesis at this stage, too small to be detected gasometrically as even 
a lowering of the respiration, but it is clear that this does not amount to 
one-tenth part of the respiration, and certainly not I per cent, of the activity 
subsequently developed. 
When the power of photosynthesis does appear, after the leaves have 
attained almost a full green colour, it develops very rapidly. 
We are forced to conclude that the first development of this function 
is not in any relation to the amount of chlorophyll produced, and that the 
amount of chlorophyll present is never a limiting factor to assimilation in 
these early stages of the assimilating organs. 
If this is so, then it must be some other component part of the photo¬ 
synthetic machinery which controls the beginning of complete functional 
activity. This part is not developed by illumination so quickly as the 
green pigment is developed, and therefore the pigment, and other parts of 
the total machinery, lie idle at the stage we have examined awaiting the 
development of the last factor. 
Finally, I would like to express my thanks to Dr. Blackman for his 
help in the experimental part and his kind interest throughout the work. 
1 Palladin : Ergriinen u. Wachsthum. Ber. dent. Bot. Ges., ix, 1891. 
