1916] CURRENT LITERATURE 419 
The extraction of the chlorophylls can be carried out with dried or fresh 
material and is based on the use of solvents containing a moderate content of 
water, the latter forming salt solutions with some of the cell contents which 
alter the condition of the chlorophyll and render it soluble in the organic 
solvent. Separation and purification of chlorophyll a and }, carotin, and 
xanthophyll is based on their differing solubilities in solvents. Little is known 
of the chemistry of the carotinoids. They are hydrocarbons, both give non- 
fluorescent solutions, stable toward alkali but easily dissociated by acids, and 
both undergo auto-oxidation. Carotin and xanthophyll have the formulae 
CyHss and CHO. respectively. 
With acids 
(C3:HaN;Mg) (CONH) (COOCH;) (COOC»H3)) ——————--> 
piggies Ga 
TH) (COOCTH \(CONOC_ FH) 
\ et 
chlorophyll a phacophytin a 
(CuHN;Mg) (CONH) (COOH) (COOH) —-> (C:H:N;) (CONH) (COOH) (COOH) 
chlorophyllin @ phytochlorin e 
and isochlorophyllin @ and phytochlorins f and g 
With alkalies 
intermediate phyllines———>intermediate porphyrins 
CyH,,NsMg —————_——— > Cp HN, 
aetiophyllin aetioporphyrin 
WittstArrer and Srott reinvestigated the question of the relation of 
chlorophyll content to photosynthetic activity of leaves in normal, chlorophyll- 
poor, vernal, and autumnal leaves. They used a modified Kreussler method 
CO, assimilated in 1 hour (in gm.). 
chlorophyll (in gm.) 
They find not only that chlorophyll is absolutely essential for photosynthesis, 
but also that it acts in conjunction with a second indispensable inner factor, 
an enzyme, which has its seat in the contact zone between plastid and plasma. 
If the chlorophyll suffers more because of external factors, the assimilation 
number rises; if the enzyme suffers more, the number falls. The enzyme 
occurs in greatest proportion in juvenile, greening, etiolated leaves and in 
yellowish green leaves, and in all of these illumination is the limiting factor, 
while temperature is the limiting factor in chlorophyll-rich leaves in the photo- 
synthetic process. Conclusions as to various steps in assimilation are drawn 
from the behavior of isolated chlorophyll as well as non-illuminated leaves 
toward carbon dioxide. Chlorophyll is not constantly decomposed and regen- 
erated, as asserted by Stoxes, neither do chlorophyll ¢ and 3, nor carotin and 
xanthophyll change into each other to any extent, as assumed originally by 
Witsrarrer. The ratio Or=3 is about constant under all conditions, 
and determined the assimilation number, 
though the ratio of falls during the course of extended experiments. A 
striking difference was noted in the behavior of chlorophyll towards CO. when 
