ii DEVELOPMENT AND ENVIRONMENT 43 



but a moderate aperture persists throughout the day, 

 followed (Fig. 39, June 8th, from noon onwards) by 

 slow closure in the late afternoon, and complete closure 

 at sunset. In such circumstances the illumination is 

 the controlling factor, and there is no water-shortage ; 

 this might be expected from consideration of the fact 

 that the existing root system has been developed to 

 cope with the demands of sunny weather. 



If this very plausible hypothesis of diurnal water- 

 shortage be correct, it must mean that the water-content 

 of the soil which is in juxtaposition with the roots has been 

 reduced at a greater rate than that at which water can be 

 restored by capillarity. During the night there must be 

 a purely physical movement of water into these semi- 

 desiccated portions of soil, since the water-shortage is not 

 apparent on the following morning. We thus obtain 

 from the Stomatograph some conception of the severe 

 strain which the plant undergoes during the torrid 

 weather of a summer in Egypt. 



The verb "to vegetate" is frequently misused as a 

 description of inert torpidity, but the daily experiences of 

 a cotton plant in Egypt almost justify this libellous 

 employment of the word. From noon onwards, this long- 

 suffering plant is neither growing, nor feeding, nor 

 transpiring beyond the necessary minimum, and possibly 

 not even breathing properly. 



The supremely injurious effect of fogs has long been an 

 article of the cotton grower's faith. It is difficult to see 

 any reason for this conviction, apart from the continued 

 low temperature which morning fogs entail, but it is 

 possible that the blocking of the stomata by condensed 

 water may have a prejudicial effect. Even so, a fog 

 should merely postpone the brief period of general activity 

 of the plant by a few hours, and not actually curtail that 

 period. On the whole it seems safer to adhare for the 

 present to the cynical explanation that most "fog" is 



