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LEWIS KNUDSON 
tration, or 0.025 mol. It was noted that 0.0125 mol. galactose is as 
toxic as 0.025 mol. galactose. The results are given in Table 2. 
Since there was variation in some of the series, the results of in- 
dividual cultures are recorded in these cases; for plants that were 
alike, the averages are recorded. 
In general the results are similar to the preceding experiment, 
though levulose is somewhat more effective than with the higher con- 
centrations of galactose. Cultures are represented in Fig. 2. 
Fig. 2. 9. Galactose .0125 
10. 
" + saccharose .025 
II. 
' + raffinose .025 
12. 
" + glucose .025 
13- 
" + levulose .025 
14. 
" + lactose .025 
15. Lactose .05 
16. Pfeffer's solution. No sugar. 
Toxicity of Mannose. — In the course of certain experiments on the 
use of various sugars by vetch (Vicia villosa) grown in water cultures, 
it was noted that mannose, supplied at a concentration of 0.025 nioL, 
killed the tips of roots that came into contact with the solution. Ex- 
periments were then made with pea and wheat to determine whether 
the effect was consistent, and agar cultures were used as in the ex- 
