Ingvar Jorgensen and Walter Stiles. 11 
CARBON ASSIMILATION. 
A Review of Recent Work on the Pigments of the 
Green Leaf and the Processes connected with them. 
By Ingvar Jorgensen and Walter Stiles. 
{Continued from Vol. XIV, p. 294). 
E. Simple Laboratory Experiments on the Leaf Pigments. 
As Willstiitter truly points out, the experiments described in 
text-books of plant physiology for the demonstration in class 
work of the properties of chlorophyll are quite inadequate. 
In preceding sections of this chapter, we have described 
Willstatter’s methods for the extraction in quantity of the leaf 
pigments. It is quite obvious, however, that the length of time and 
large amount of material and reagents required for these extrac¬ 
tions, render their use scarcely possible for ordinary class work. 
We have therefore brought together in this place a number of 
easily performed experiments which amplify the collection of 
examples given in Willstatter and Stoll’s book. 
The performance of these experiments will not only lead the 
student to clearer ideas about the chemistry of the leaf pigments, 
but will also give an opportunity for that chemical and physical 
manipulation which is becoming increasingly necessary to the plant 
physiologist, but for the practice of which there is no great 
opportunity in most other parts of a plant physiology course. 
Preliminary. It will be found of great convenience for class 
work to collect in the summer every year a quantity of nettle 
leaves. These are dried at air temperature; they are spread out 
on sheets of paper and a sheet of paper placed on top of them to 
prevent dust from falling on them, and to prevent undue exposure. 
They are then ground up finely and dried completely for several 
days at a temperature of 30° to 40 ft C., in an incubator. 
The powder so obtained is kept in a stoppered bottle. So 
prepared, the powder retains for a long time the leaf pigments 
unaltered in quantity and quality. 
Any further drying required must be carried out by placing the 
leaf powder in a vacuum desiccator over sulphuric acid. This 
procedure is necessary for instance when it is required to show that 
pure solvents do not extract the pigments from dry leaf powder. 
In this case it is also necessary that the solvents should be as water- 
free as possible. Ordinary solvents may have to be redistilled over 
quick-lime, calcium filings, etc. 
