r,S EGYPTIAN AGRICULTURE. 



producing heat and acids. The acids resulting from the 

 decomposition of organic matter are dissolved in the soil 

 water and give it the power to attack and weather the 

 mineral foods for the plants. In fact, unless slightly acid, 

 the soil water is of little use as a weathering agent and 

 plants would obtain but little food. Without the activity 

 of these organisms, humus and organic manures would 

 be of no value, and the mineral particles of the soil would 

 form practically an inert mass changing too slowly to 

 admit of the growth of anything but the most meagre 

 crop. 



Before closing this short consideration of the soil, it is 

 necessary to glance at the position of the plant in the soil. 

 The relation existing between the plant and soil can be 

 best explained diagrammatically. The following diagram 

 is a supposed section through the plant root and soil. 



FIG. 4. ROOT HAIR IN THE SOIL. 



The soil particles are sketched and shaded ; the soil water 

 is represented by shading ; the air by unshaded spaces. 

 A root hair, much magnified, leaving the root extends 

 through the section. For the sake of simplicity and clear- 

 ness certain unimportant factors will be overlooked. 



In a well drained soil the water is present in the pores 

 of the porous particles, in the smaller interspaces and as 



