W. F. Be w LEY 



127 



constantly, was not available, inoculated plants (hypocotyl stab) were 

 placed in certain positions in the experimental houses, corridors, etc. 

 under as different average temperature conditions as could be arranged. 

 Twelve plants were placed in each position, and the average temperatures 

 were calculated from readings taken twice daily from maximum and 

 minimum thermometers placed besides the plants. The final observations, 

 shown in the following tables, were taken 21 days after inoculation, and 

 where figures are given each represents the average of data obtained 

 from 12 plants. 



Table IV. 



Ratio of wilted to total leaves 



6:10 



3 :10 



1 :10 



:10 



:10 



While the results obtained are open to criticism because of the wide 

 range of temperature to which the plants were submitted in any one 

 position, certain empirical facts emerge which have been fully confirmed 

 by observations in commercial nurseries. Chief among these is the bene- 

 ficial eftect which shade and temperatures above 24-0° C. have upon 

 plants suffering from Verticillium wilt. Table IV shows that average 

 temperatures of 16-6° C. and 20-0° C. are favourable to the rapid progress 

 of the disease, that of 12-5° C. is unfavourable, while that of 2.5° C. 

 practically inhibits it. It will be seen that the organism has travelled 

 most rapidly up the stem, as indicated by the browning of the wood, at 

 16-6° C. and 20-0° C, and at these temperatures also complete wilt 

 occurred most quickly. The results shown in Table V, while confirming 

 the temperature relations, show^ the beneficial effect of shade. While 



9—2 



