THE PLANT 



37 



horizontally almost as far as the tap-root descends ver- 

 tically, though not quite so far if other things are equal, 

 and are important contributors to the plant's sustenance 

 until the soil layer which they occupy is too crowded with 

 roots from adjacent plants to be of much use. 



June5*- h -Jur%el9h June29'NJuly 13 

 First Flower-buds First Flowers 



Flowering reaching Second picking 



maximum Flowers 



First picking, length F.rst pickind.stn-nth 



being determined. being determined. 



Soil Surface 



56 below 

 surface I 



FIG. 7. ABSORPTION OF WATER BY THE ROOT SYSTEM. 



From actual experimental data taken in field crop at Giza, 1912 (see Journal 

 of Agricultural Science, vol. iv., 1913, for the full account). 



The black areas represent the water-loss during a fortnight, and are thus 

 practically a picture of the activity of the root-system at various 

 depths, for four periods of the year. 



Approximate dimensions of stem and root at each period are indicated. 



Surface soil loses much water by direct evaporation in the early part of the 

 season. Later on the plants shade the surface, and most water is derived 

 from three to four feet below the surface at the time when the first picking 

 is ripening. 



The zone of most importance in the root system thus 

 shifts steadily downwards as the season goes on, until, at 

 the time when the first picking is ripening in Egypt, the 

 crop is actually taking more water from a depth of four 



