Oct. 29, 1921 Relation of Soil Temperature to Onion Smut 



245 



pots were removed on the thirtieth day. The relative dry weights of 

 roots and tops then secured are shown in Table V and those of the Red 

 Globe are graphed in figure i. 



While the temperature relations of the two varieties were alike in their 

 main features, there was an interesting minor difference, possibly indica- 

 tive of the better adaptation of the Red Globe for northern culture and of 

 the Yellow Bermuda for southern. In both cases with these onions, as 

 indeed holds generally in our experiments with other plants, the best 



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Fig. I. — Relative developments of dry weight in tops and in roots of Red Globe onion as shown at end of 

 30 days' growth in a series of culture pots kept at the several soil temperatures indicated, with all other 

 factors, including air temperature, alike for all. Note that the best root development occurs at the low 

 temperatures (12° to 15° C.) whereas the tops are forced more strongly at higher temperatures (20° to 25°). 



root development occurs at relatively lower temperatures (12° to 20° C.) 

 while best top development occurs at higher temperatures (20° to 25°). 

 When the varieties are compared, it is seen that with the Globe both 

 roots and tops grew relatively better at somewhat lower temperatures 

 than did those of the Bermuda. Thus the data at 30 days show the 

 maximum root development of the Globe at 14° while that of the Ber- 

 muda was at 20° ; with tops the maximum was at 20° for the Globe and at 

 25° for the Bermuda. 



