512 CLARIFIED AND UNCLARIFIED SEWAGE. 



that all plants require the soil as well as the atmosphere 

 in which they grow to correspond in temperature with 

 that of the countries in which they are natives. It has 

 also been already shown that the mean temperature of the 

 soil should be above that of the atmosphere." Again (p. 

 137) "Those who imagine that the advantage of drainage 

 arises from the removal of stagnant water or any such 

 cause alone, overlook the great and important fact that 

 drained land in summer is from 10 to 20 warmer than 

 water-logged land." Again (p. 138) "As scarcely any of 

 our cultivated crops are natives of countries so cold as our 

 own, it is manifest that they all require to have the earth 

 warmed for them, or are much the better for it." 



The free access of air to the soil in which plants grow 

 is not less important than that of heat. 



"The roots of plants, notwithstanding their under- 

 ground position, are subject to the action of the air which 

 permeates the earth. We have long known that trees 

 suffer if we inter the base of the stem in such manner 

 as to exclude the air from their roots. The roots suffer 

 more from contact with stagnant water, even when richer 

 in nutritive matters, than when in contact with running 

 water, because the latter brings them a constant supply 

 of oxygen. M. Th. de Saussure found that plants whose 

 roots .were placed in gas deprived of free oxygen died at 

 the end of a few days, whilst those placed in contact with 

 the atmosphere lived and prospered." Physiologic Vege- 

 tale, Tome L, pp. 136-137. 



Many years ago I used " unclarified " sewage exten- 

 sively, and for a lengthened period. The results were not 

 satisfactory until I adopted the practice of stirring the 

 surface of the soil after every application of the sewage. 

 The results then exceeded my expectations, but when 

 estimated were not found equivalent to the largely in- 

 creased cost of labour. Afterwards the sewage was 

 clarified by the use of quick lime and used for a 

 lengthened period in this state ; this was judged better 



