410 
R. B. HARVEY AND R. H. TRUE 
By means of the Grignard reagent Willstatter and Stoll were able 
to introduce magnesium into the substance aetioporphyrin C31H36N4 
to form aetiophylHn C3iH34N4Mg, one of the cleavage products of the 
chlorophyll molecule. The results of experiments here presented seem 
to indicate that the introduction of magnesium into the compounds of 
the leaf takes place to a greater degree when there is sufficient illu- 
mination to cause a green coloration, that is, the squash requires light 
for the later steps of chlorophyll synthesis and these steps are asso- 
ciated with the removal of magnesium from the field of toxic action. 
No quantitative measure of the amount of chlorophyll compounds 
present has been obtained on account of their instabiHty and complex- 
ity. However, calculations using the formulae found by Willstatter 
indicate that the increased amount of magnesium used in the light is 
well within the limits of the amount used for chlorophyll synthesis as 
determined by Willstatter in nettle leaves. 
In testing the toxicity of ferric chloride solutions under similar 
conditions, no differences were observed between cultures grown in 
the light and darkness. 
Summary 
The minimal toxic concentration of magnesium nitrate for the 
squash grown in water cultures was found to be I2^n X 10-6 in the 
dark and 200n X 10-6 in the light. The increase in the minimal toxic 
concentration is probably correlated with the removal of magnesium 
from toxic compounds to form chlorophyll. 
Bureau of Plant Industry, 
U. S. Department of Agriculture. 
LITERATURE CITED 
1. Willstatter, R. Chlorophyll. Jour. Amer. Chem. Soc. 37: 323. 1915. 
2. Willstatter, R., & Stoll, A. Untersuchungen iiber chlorophyll. 1913. 
3. Mameli, E. Atti Soc. Ital. Progr. Sci. 5: 793. 191 1. 
4. Mameli, E. Atti 1st. Bot. Univ. Pa via (2) 15: i. 1912. 
