30 THE DEVELOPMENT OF RAW COTTON 



Under the climatic conditions in which cotton finds its 

 most suitable temperatures, the mere evaporation of 



water from a water-surface is usually very 

 Water and M h during the day and the total - wate r- 

 the Crop. 



surface " of all the leaves in a field of cotton 



is enormous. Some idea of its magnitude may be 

 gathered from the fact that the author and Mr. Hughes, 

 working quite independently, both showed that normal 

 fields of Egyptian cotton in a normal year (1912) evapor- 

 ated amounts of water which increased steadily up to 

 fifty tons of water per acre per day. This figure is almost 

 incredible, being twice as high as the amount of water 

 actually supplied to the land in irrigation the duty of 

 water in Egypt being twenty-four tons but the deficiency 

 is made up by water withdrawn from the water-table. 

 When expressed in terms of single plants, it is even more 

 incredible i.e., about three pints per plant per day. 



There can, however, be no shadow of doubt as to the 

 truth of the figures, which in both cases were obtained 

 by directly measuring the changes of water-content in 

 the soil of a field. They throw into vivid relief the severe 

 nature of the " water-strain " which the plant has to 

 undergo each day of its life. 



One of the first evidences of this strain was the writer's 

 discovery that from quite the beginning of its career the 

 cotton seedling did not grow in sunshine, all 

 8 Q water being used in keeping the plant 



cool as long as possible ; and when the soil 

 supply began to give out, at some time during the after- 

 noon, the stomata closed. 



