78 SOILS 



coated with hot wax to prevent evaporation from it. 

 A plant, then, is a pump; there is a cloud of in- 

 visible water vapour rising from every grass blade 

 and every cotton leaf. The value of some plants 

 as pumps compares quite favourably with the 

 pumps we buy. Eucalyptus trees are sometimes 

 used for draining malarial swamps; willows 

 planted at the mouth of the sink drain keep the 

 soil from getting soggy. 



RAINFALL INSUFFICIENT OR UNEVENLY 

 DISTRIBUTED 



With these figures on the actual amount of water 

 that a soil may lose in producing certain crops, and 

 with this explanation of where so much of it goes, 

 the farmer may now get from the nearest Weather 

 Bureau a statement of the average amount of water 

 that falls upon his soil each year or he may consult 

 the general rainfall map on another page. Then 

 compare the two sets of figures. At first sight, it 

 may look as though there ought to be no difficulty 

 in watering the crop; the rainfall may be thirty 

 inches and the crop may use but thirteen. But 

 how much of this rainfall conies during the months 

 when the crop is growing ? How much of the rain- 

 fall previous to me planting of the crop can be 

 saved in the soil? These two questions must be 

 answered. The weather man will answer the 

 first; only the farmer can answer the second, 

 for it depends entirely upon the kind of 

 soil he cultivates and upon the way he 

 handles it. 



A comparison between the average rainfall dur- 

 ing the growing season, say from April 1st to Sep- 

 tember 15th, and the amount of water needed by 



