1918] FIELD CROPS. 339 



tions extending over the period of 1909-1913 and at g;everal centers in Egypt 

 forms the basis upon which the studies were made, 'the factors were studied 

 chiefly in their effects upon the flowering curve, which represents the daily rate 

 of flowering of an average plant, and the relation between the formation of this 

 curve and the antecedent growth processes and subsequent yield outlined. 



The flowering curve and consequently the yield ciu've were shown to have a 

 typical form under good cultural conditions. Poor cultivation is defined as any 

 condition that allo'vvs a factor to become limiting when it need not be so, thereby 

 deforming the curve. 



The differences of behavior of various cotton crops appeared to be inevitable 

 consequences of the knov.n environmental conditions, provided only that due re- 

 gard be paid to the distinction in time between the causation of any effect and 

 its manifestation. To denote this latter distinction the author uses the term 

 " predetermination. " Daily fluctuations of the flowering curve constitute an 

 example of predetermination, since they are controlled by weather conditions 

 which obtained a month before the flowers opened, and simultaneous fluctua- 

 tions in the same direction may be shown by all cotton fields in Egypt. 



Deductions are presented v.-ith regard to the function and dimensions of the 

 absorbing part of the root system as distinct from the merely conducting por- 

 tions. By comlwniug the analyses made in these studies with data concerning 

 the commercial aspect of Egyptian cotton it has been shown that root asphyxia- 

 tion produced by a rising water table is the principal cause of the deteriora- 

 tion in yield per acre which the crop has suffered. 



In discussing the physiological outlook essential for an effective analysis of 

 agriculturtd yield, the author asserts that the method of study employed in 

 these investigations is a matter of adjustment depending only on the choice of 

 cardinal points for observation in the crop to be studied, and that a superposi- 

 tion of the continuous observation method upon the scattered small-plat methd 

 may be expected to link plant physiology more closely to agriculture. With a 

 proper conception of the law of limiting factors, as advanced by F. F. Black- 

 man, and of the frequent predetermination of their effects, there is thought to 

 be abundant opportunity for advances in the knowledge of so-called " crop 

 physiology " by applying these methods of continuous registration to plant de- 

 velopment. The liiultations of the plant-development curves as tools for pur- 

 poses of research are (1) that the data required for their construction must al- 

 most invariably be obtained daily throughout the season, since the day is the 

 real time limit in which a plant measures its experiences, and (2) that they 

 necessitate considerable labor. Opposed to these disadvantages is the fact that 

 they abolish the probable error of plant experiments, thereby achieving good 

 results with controlled areas otherwise far too small if the yields wei*e not thus 

 analyzed. The author continues : 



" It is probable that the solution lies in compromise, by first establishing a 

 set of standard data, as complete as possible, for any given crop and district, 

 with which any subsequent observations of salient features could be compared. 

 The establishment of such a set for the Gheezeh Cotton Experiment Station was 

 one of the author's chief aims. . . . The desired extension of the observa- 

 tions to minor outlying stations in other parts of Egypt would have provided 

 not only a system of precise crop reporting, on the lines of a weather report, but 

 also a system of crop forecasts. 



" Our principal general conclusion is, therefore, that Blackman's law of 

 the limiting factor provides the key by which the intricate relations of any 

 crop to its environr^ent may be satisfactorily unlocked, provided only that these 

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