l^C 



In summary of all results it may be said that 

 Goleus is injured in from 2 to 10 days after the normal 

 soil atmosphere is replaced by an atmosphere of nitro- 

 gen. When the concentration of oxygen in the soil air 

 is diminished injury also occurs, possibly a little 

 less quickly. Apparently the decrease of oxygen supply 

 suffered when a plant is sealed-in but with the outlet 

 tubes left open is also sufficient to cause injury, but 

 in this case the appearance of the injury is clearly 

 later than when the exclusion of oxygen is complete. The 

 symptoms of injury are wilting and a cessation of water- 

 intake by the plant. Usually the water- intake ceases 

 a few hours or more (sometimes several days) before wilt- 

 ing of the leaves is perceptible. 



On examining the roots of plants which had 

 been injured by exclusion of oxygen the root-systems 

 were found to be dead and decayed. When the injury was 

 recent the visible decay of the roots was partial. Roots 

 were determinately dead only in parts of their length, 

 regions of brown discoloration alternating with regions 

 of apparently healthy root. After long-continued ex- 

 clusion of oxygen the entire root-system was invariably 

 found to be dead. In all of the plants which were first 

 injured and then revived by the re-admission of air or of 

 oxygen, the original root-system was found to be dead. 

 The recovered plant was supplied by a new root-system 

 starting always from the lower end of the stem. In no 



