98 BOTANICAL GAZETTE [February 



containing Uvo carboxyl groups, only one of which is linked with the 

 amid group. The behavior of the seedlings grown in solutions of 

 aspartic acid is in harmony with this fact. The injurious effect of 

 the aspartic acid suddenly disappears as soon as diluted below loo ppm. 

 and the gradual disappearance of toxic effects is not sho^ii. The 



seems 



carboxyl groups which it contains. 



The physiological action of neurin, cholin, and betain presents 

 some interesting facts bearing upon the relation of toxicity to chemical 

 structure. It will be noted, by reference to the structural formulae for 

 these compounds, that they differ only in one of the groups. Neurin 



ms 



ethylene group, and has one carbon atom oxidized to the primary 

 alcohol stage ; finally in betain the alcohol group is oxidized to car- 

 boxyl with subsequent sphtting-off of water. Corresponding to the 

 increased degree of oxidation in these three compounds, there is a 

 decrease in their toxicity, neurin being the most toxic, and betain 

 being absolutely non-toxic in concentrations less than looo ppm. 



On account of the slight solubility of two of the four urea deriva- 

 tives employed, it is not possible to make comparisons of their 

 physiological actions. The compounds which contam the purin 

 group did not appear to be toxic. Guanidin, however, is distinctly 

 toxic, and alloxan moderately toxic. 



The pyridin compounds employed are all toxic, some of them 

 being fatal to wheat plants in relatively small amounts. Ppidin 

 itself appears to be relatively less toxic than any of the other related 

 compounds studied. It was not fatal at a concentration of looo ppm. 

 and only injured the tops slightly in concentrations of loo ppm. and 

 less. The introduction of methyl into the pyridin appears to increase 

 slightly its toxicity (picolin). The addition of more hydrogen to p}Ti- 

 din (reduction) produces a marked increase in its toxicity, as is shown 



-^i action of piperidin, which may be regarded as 



. This fact supports what was said on a previous 



page concerning the decrease of toxicity accompan}Tng the oxidation 



of neurin, cholin, and betain. Chinolin appears to be somewhat more 



toxic than pyridin, as might be expected from its rpsemblance to 



