in DEVELOPMENT AND ENVIRONMENT 65 



demonstrate for the first time the effect of increasing the 

 head of water on the Delta Barrage and so immersing the 

 lower roots sooner than would normally be the case, in 

 the land lying up-stream. 



1910 1911 



:o-2o - 



June July August September October 



11 18 25 2 9 16 23 30 6 13 20 27 3 10 17 24 1 8 15 22 29 



FIG. 45. MEAN FLOWERING CURVES IN FIELD CROP. 



On same land, with same variety, in three Successive years, at Giza. 



X = Date on which Roda Gauge reached 16 m. A.S.L. 



Decaudation due to rise of sub-soil water over roots. See Figs. 30, 35, 38, 



and 47. 



The boiling curve. Curves plotted to show the 

 number of bolls opening each day in the same way as for 

 the flowering curve, should be identical with them, if all 

 the flowers which opened were ripened into bolls. Such 

 perfection has never been obtained by any of the author's 

 plants. Some of the flowers -are always shed, and the 

 ratio of bolls formed to flowers opened has never exceeded 

 90 per cent., and has been known to fall almost to zero. 

 To take an extreme example, a certain plant, otherwise 

 quite healthy, in the year 1909, ripened three bolls out of 

 a total of 746 flowers which opened before the middle of 

 September. 



The early part of the boiling curve, formed by flowers 

 which have opened at the beginning of the Critical Period, 

 is usually identical with the form of the originating flower- 

 ing curve (Fig. 30), but after the first few weeks it 



