TOXICITY OF GALACTOSE AND MANNOSE FOR GREEN PLANTS 43 1 
by addition to the nutrient solution or by addition of another sugar 
solution. For example, to obtain a solution containing 0.25 mol. 
galactose + 0.025 mol. saccharose, it was necessary to mix equal parts 
of 0.5 mol. galactose and 0.5 saccharose. The volume of the medium 
in each tube was 25 cc. Sterilization was effected by autoclaving at 
fifteen pound^ pressure for fifteen minutes. 
All the sugars used, with the exception of arabinose, were supplied 
by Dr. C. S. Hudson, in charge of the carbohydrate laboratory, 
U. S. Bureau of Chemistry, and are stated by him to be of very high 
purity. The arabinose used was a Merck reagent. 
Character of the Injury. — The injurious action of galactose is made 
evident first in the roots. The primary root coming in contact with 
the agar may first become brown and in a few days death results. In 
other cases the tip of the root is killed and this stimulates the pro- 
duction of a large number of lateral roots, the tips of which, on coming 
in contact with the agar medium, are soon killed. A short primary 
root with many laterals results, the appearance of which is somewhat 
centipedal. Two plants in the same culture may, however, vary in 
the manner of injury, and the presence of certain sugars may alter 
the extent of the injury. 
For the sake of clearness and definiteness, it seems desirable to 
describe the injury by a numerical system as well as by root lengths- 
Accordingly the following key is given: o, no injury; i, primary root 
tip killed, laterals not injured; 2, the primary root tip may be killed, 
but the laterals may attain a length of a few centimeters and then 
growth is stopped or the roots are killed; 3, the primary root may 
penetrate the agar, but becomes brownish and five or six centimeters 
long; 4, the primary root may attain a length of a few centimeters, but 
becomes brown in color and the laterals do not grow beyond 0.5 cm. ; 
5, the primary root tip is killed and all laterals suffer likewise; 6, the 
primary root is entirely killed. 
Antagonistic Action.' — In the following experiment the galactose 
was supplied at a concentration of 0.025 mol. and the other sugars 
were used at the same concentration. In order to demonstrate con- 
clusively that the total concentration was not responsible for any 
toxicity, a few cultures were made with the nontoxic sugars supplied 
at 0.05 mol. The experiment was begun on January 29, 191 7, and 
concluded on February 13, 1917. The cultures were placed- in the 
greenhouse and grown in the light. All cultures were made in trip- 
