THE PLANT 



33 



soil might result from placing the plants widely apart, 

 but this, beyond a certain lower limit, would reduce 

 the yield per area, since the increase in size of the plants 



I rrigated 



Fic. 4. DAILY GROWTH OF THE MAIN STEM. 

 Actual experimental data. 



Variety, Afifi; site, Giza; ordinary field crop; year, 1911. T, upper curve, 

 represents nightly minimum temperatures;^, lower curve, represents 

 the amount of elongation of the main stem in each successive twenty- 

 four hours. 



Until the end of June the two curves are similar i.e., growth was limited 

 by night temperatures, except upon days which are marked in the 

 diagram by eight feathered arrows. 



These arrows denote days when the maximum temperature hi the previous 

 afternoon had been too high (over 36 C.), so inducing the formation 

 of a " heat-poison " in the plant, and thus reducing growth during the 

 following night to less than the amount expected (indicated by dotted 

 lines). 



At the end of June the effects of soil-water were just beginning to be felt 

 as the plants grew larger and took more water from the soil. Pre- 

 viously there had been more water than the plants could remove. 



Further, this shortage of water induced " self -poisoning " in the terminal 

 bud of the main stem, and its growth ceased ultimately to respond 

 even to irrigation. The terminal buds of the branches are similarly 

 affected later. 



would not compensate for the smaller number of 

 plants on the area (Fig. 6), and, moreover, surface soil 

 dries up more quickly than deep soil, so that it would be 



3 



