THE PLANT 3d 



stages of growth in the summer. On the other hand, 



the presence of salts in the soil is often a serious factor 



in Egyptian cotton-growing, whether the 



salt is common sodium chloride or the more 

 Soils. 



objectionable carbonate, or " black alkali." 



The action of salts is relatively simple ; an excess of them 

 prevents water-absorption by the root through simple 

 physical control, while less amounts may in some cases 

 act poisonously. Under field conditions one or two 

 interesting points arise. Since salt is concentrated at 

 the surface of the soil by evaporation, and washed down 

 again by surface watering, the surface soil may be so salt 

 as to hinder the germination of seed ; but any odd seed- 

 ling which may manage to work its tap-root down into 

 the sweeter soil below will flourish. Thus, a perfectly 

 healthy plant may be growing in the middle of a salted 

 patch of land. Another curious feature of cotton with 

 regard to common salt is that it takes up quite large 

 amounts from relatively sweet soil, the concentration 

 attained in the cell sap being different with different 

 kinds of cotton, and amounting in the most " salty " 

 kinds to nearly as much as in typical salt-marsh weeds 

 which are washed by spray from the sea. 



In most countries other than Egypt the manurial compo- 

 sition of the soil is an important factor, but one which has 

 never been properly investigated, with the 

 result that most conflicting opinions are held. 

 In saying that no proper investigations have been made, 

 the author would not wish to discredit the large amount 

 of experimental work which has been carried out in this 



