192 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



The amount of carbon dioxide in the soil air, which, as we have 

 just seen, indicates the rate at which it is produced, follows the soil tem- 

 perature during the winter months, but not during the summer ; indeed, 

 during hot weather the amount is distinctly low (fig. 63). It does not 



Mesa temperature of soil 6" depth for 24 hours 



prior to sampling O 



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show any very close connexion with the moisture content, but it is 

 more closely related to the rainfall (fig. 64). 



Thus it appears that rain does something more than add water 

 to the soil, and an interesting problem is re-opened which has in the 



