58 Lewis Knudson 



while in each of the other six were sown two seeds of vetch. The 

 plants were grown for thirty-five days, and the solutions were then tested 

 for glucose by means of Benedict's reagent. All the check, solutions 

 showed distinctly the presence of glucose; two of the culture solutions 

 gave no tests whatsoever for glucose, three showed the merest trace, 

 and the sixth, having a poorly developed plant, gave a fairly good indication 

 of the presence of the sugar. The culture solutions were all tested for 

 sterility by drop transfers to tubes of agar containing 0.5 per cent of 

 glucose and Pfeffer's solution. In no case was any contamination shown. 

 The culture solutions being free, therefore, from yeasts and bacteria, 

 as well as from fungus mycelium, the conclusion is warranted that the 

 glucose is absorbed by the vetch plant. 



TOXICITY OF GALACTOSE FOR HIGHER PLANTS 



In the course of these investigations it was noted (Knudson, 1915) that 

 the sugar galactose was injurious to vetch, peas, corn, and wheat at a con- 

 centration as low as 0.0125 per cent. The injury was noted particularly 

 in the roots. With higher concentrations the primary root tip coming in 

 contact with agar containing galactose was killed, and lateral roots stimu- 

 lated to formation met the same fate; so that ultimately a much-branched 

 root was obtained. In case the entire primary root came into contact 

 with the galactose-containing 'agar, it first assumed a brownish appearance 

 and soon afterward died (Figs. 10 and 11). With Canada field pea it 

 was noted that both lactose and rafhnose increased growth. These two 

 sugars, on hydrolysis, yield galactose as one of their products. It would 

 appear, therefore, that galactose in the presence of glucose exerts no 

 injurious effect. This was found to be the case. Glucose at a concen- 

 tration of 1 per cent almost completely inhibited the toxic action of 1 

 per cent of galactose. In the previous experiments also it was noted 

 that 1 per cent of galactose is antidoted by 1 per cent of glucose, but 

 no other concentrations of glucose were employed. Accordingly an 

 experiment was planned in which the galactose was to be maintained at 

 a constant value and the concentrations of glucose were to be varied. 

 Details of the experiment follow: 



Large test tubes were used as culture vessels, each containing 33 cubic 

 centimeters of the medium to be tested. The nutrient medium was 



