Carbon Assimilation. 
177 
Willstatter, however, expresses this opinion in a far more 
dogmatic way, postulating that the chloroplast is the seat of a photo¬ 
chemical reaction and that the product formed in this reaction is 
subjected to an enzymatic action which takes place at the boundary 
between chloroplast and plasma. In this latter process oxygen is 
t 
supposed to be evolved. His contention is that the efficiency of the 
assimilatory process depends not only on the amount of chlorophyll 
but also on the amount of enzyme, and in his investigation he has 
examined extreme cases where either chlorophyll or enzyme are in 
excess. 
The very great importance of Willstatter’s work lies in the fact 
that for the first time quantitative estimations of the pigments have 
been made; in an earlier chapter we have stated in some detail the 
methods employed by Willstatter and also pointed out how unreliable 
were the estimations of all of the earlier workers. The principle 
used in the analysis is the saponification of the leaf extract with 
alkali and the subsequent abstraction of the yellow pigment with 
ether. The chlorophyllin solution is then compared colorimetrically 
with standard solutions. Thus the disturbing influence of the 
yellow pigments is avoided ; however, it must he pointed out that 
the information obtained only holds for the chromogen complex ; 
as regards the phytol part of the chlorophyll molecule which is 
split off in the saponification we do not get any information. 
Willstatter’s experience from earlier investigations where the 
pigments were estimated in leaves collected at various times of the 
day and at various seasons led him to the conclusions that the 
amount of pigment is not altered during the processes of assimilation; 
this view is confirmed here, for Willstatter finds no appreciable 
difference in the amount of pigments as the result of assimilation. 
Of course it has been assumed before Willstatter’s time that 
the assimilation varies with the amount of chlorophyll, hut it had 
not been possible definitely to estimate the chlorophyll content or 
to differentiate between the part played by the chlorophyll and the 
part played by the plasma. 
Thus, for instance, Weber (1879) found that equal areas of the 
leaves of different plants under the same conditions had different 
assimilatory powers. Haberlandt (1882, and see 1914) explained 
Weber’s results by determining the number of chloroplasts per 
unit area in the plants used by Weber and showing that there is a 
parallelism between the assimilatory activity and the number of 
chloroplasts. His results are exhibited in the following table. 
