51 



procedure for aeration is embodied in most directions for 

 water- cultures and is usually employed. 1 This general 

 opinion is re-inforced by the observation of Kosaroff^ 

 that the passing of a stream of hydrogen through the 

 culture solution decreased the absorption of water by 

 plants of Phase olus multiflorus. On the other hand 

 Pember^ has found that the passage of a stream of air 

 through the culture solution has no effect on the growth 

 of barley and Free 4 has obtained similar negative re- 

 sults with buckwheat, the passage of streams of air, 

 nitrogen and oxygen being alike without determinable 

 effect on the growth rate or the total production of 

 dry matter. It seems probable that the effect of aera- 

 tion in water-cultures, as in soil, is complex and 

 varies with the individual nature and circumstances of 

 each culture. The effect of carbon dioxide in water 

 culture will be discussed on page ^^ below. 



1. See Pfeffer,- Physiology of Plants, 

 vol, 1, p. 420 (1900); Ehrenberg,- Bodenkolloide, p. 

 516 (1915). For an excellent review of the litera- 

 ture of work with water- cultures see Tottingham,- 

 PhysL ol. Res. 1: 138-159 (1914). 



2. Diss., Leipzig, pp. 51-57 (1897). 



3. Rhode Island Agr. Sxp. Sta., Bull. 169; 

 pp. 24-25 (1917). 



4. Johns Hopkins Univ., Circular : 



(lyi7). 



