igoS] SCHREINER &- REED— TOXIC PLANT CONSTITUENTS 75 



tions for growth were the best, each experiment was continued for 

 eight to ten days, but during the cloudy winter weather some of 

 the experiments were continued for twelve to fourteen days; the 



umn 



of Table II 



Two and sometimes three criteria of growth were employed, viz., 

 transpiration, green weight, and turgidity, no one of which can be 

 regarded as absolute; but they usually agree in indicating the order of 

 results, which was the point sought in the experiments. The jars con- 

 taining the water cultures were closed with cork stoppers notched and 

 carefully fitted to receive the seedling, so that there was practicaUy 

 no chance for loss of water except that transpired by the seedlings. 

 Therefore, the loss in weight of the cultures represents verj- closely 

 the amount of water transpired by the plants, and in the case of 

 wheat the transpiration has been shown by Ltongstox (:o5; and 

 Jensen (:o7) to be a very accurate measure of gtovnh when com- 

 parisons are made with control cultures. Transpiration is more 

 nearly proportional to the growth of both roots and tops, while the 

 green weight is not at aU an indication of root growth and is liable, more- 

 over, to some error in indicating the actual growth of tops. In com- 

 puting the effects of the toxic agents employed, the transpiration 

 figures are believed to be a more reliable indication of the gro^^th of 

 wheat, so far as the entire plant is concerned, than the weight of the 

 green tops. ^lany of the substances employed produced the greatest 

 effect upon the roots of the seedlings, and it was found that the trans- 

 piration record was a better indicator of the growth in such cases than 



the green weight of the tops. 



The weight of the tops or of the entire plants in the fresh condition 

 was taken as a second means of measuring their growth and as a 

 means of comparison with the control plants. 



The condition of the root tips was also noted as an aid in deter- ^ 

 mining the lethal concentration. When kiUed, the root tips lose their 

 turgidity and soon become slimy. Before this ensues they S^^^Y 

 show indications of injury by discoloration in the region occupied by 

 the most actively growing cells or meristem. In some solutions the 

 tips stop elonga'ting and become swollen, with more or less simui- 

 taneous discoloration. 



