THE TOXICITY OF GALACTOSE AND MANNOSE FOR 
GREEN PLANTS AND THE ANTAGONISTIC ACTION 
OF OTHER SUGARS TOWARD THESE^ 
Lewis Knudson. 
In experiments concerned primarily with the utilization of certain 
sugars by certain green plants (Knudson, 1915, 191 6), the noteworthy 
fact developed that, while other sugars may be of benefit, galactose is 
toxic. The injurious effect was manifested in a killing of the root or a 
retardation of root growth, depending upon the concentration of 
galactose employed. It was observed, furthermore, that glucose 
can antidote the toxicity of galactose, but this antagonism occurs only 
when the glucose is present at a concentration equal to or greater than 
that of the galactose. So far as the writer has been able to determine, 
this is the only recorded case of a hexose sugar being injurious to 
plants and of antagonism among the sugars. 
In view of the fact that glucose exhibited such a marked antago- 
nistic action toward galactose, it seemed advisable to extend further 
the investigation to include various other sugars, A considerable 
number of experiments have been made to this end and the paper 
here presented records briefly the results obtained. 
Methods. — For the experiments either Canada field pea (Pisum 
arvense L.) or wheat {Triticum sativum L.) was used. Th6 plants were 
grown in all cases under conditions insuring freedom from micro- 
organisms. For this purpose the plants were grown in culture tubes 
200 mm. X 20 mm. in size, on a nutrient agar medium. Pfeffer's 
nutrient solution, slightly modified, was made up as follows: Ca(N03)2, 
4 grams; KNO3, I gram; K2HPO4, i gram; KCl, 0.5 gram; MgS04, 
0.5 gram; FeCls, 20 milligrams; distilled water, 12 liters. The agar 
used had been previously rinsed three times in distilled water and then 
air-dried. One percent of agar was used. The medium is faintly 
alkaline to methyl red. The different sugars were dissolved in this 
medium and stock solutions were made up of double the concentration 
of sugar used in the experiments. Dilution of the sugar was effected 
^ Contribution from the Laboratory of Plant PKysiology, Cornell University. 
430 
