494 BOTANICAL GAZETTE [june 



sugar. Meyer has made determinations of the amounts of car- 

 bohydrates during the course of the day and night. Working with 

 the leaves of Tropaeolum, he found that reducing sugars were at a 

 minimum during the day but started to increase with nightfall. 

 Analyses of tomato leaves yielded similar results ; when the weather 

 was bright the maximum reducing sugar content was found at 

 1:00-2:00 A.M. During dark weather this gradation was found 

 to be much disturbed, as would be expected. The following figures 

 were secured from the tomato leaves during such a period: 



Reducing sugars; weather very dark and rainy 



1:30 P.M., 0.414 per cent, calculated as dextrose (net weight) 

 5:30 P.M., 0.335 per cent, calculated as dextrose 

 11:30 P.M., 0.285 per cent, calculated as dextrose 



Presence of other factors made it impossible to ascertain what 

 effect these variations had on resistance. There seems to be little 

 doubt that the glucose in the plant acts as a protective agent 

 'against injury by cyanide. Considering glucose to have a direct 

 effect, there are several possibihties concerning the manner of this 

 action, (i) It may protect the plant by supplying an excess of 

 molecules to unite with the cyam'de entering. Cyanide does unite 

 readily with glucose. (2) There is much evidence in physiological 

 experimentation, with both plants and animals, showing that an 

 excess of glucose present will temporarily take the place of missing 

 oxygen. Asphyxiated animals produce glucose in excess amounts, 

 other compounds being broken down. Plants, in absence of oxygen, 

 behave normally for a time when glucose is supphed. It may very 

 readily be that the protective action of the glucose is an indirect one, 

 working through other channels. Thus it may possibly modify 

 stomatal action. 



What goes to make up a resistant plant, and under what con- 

 ditions is it most resistant ? We have given but Httle attention to 

 the first of these questions ; hence the broad problem of why certain 

 species of plants are much more resistant to cyanide than others 

 will be left without attempting an answer. Rather exhaustive 

 comparative studies seem to be the only possible way of solving this. 



