203 



have an open inner structure, permitting the storing of larger quantities of 

 air within the body and suggesting the facihtation of internal respiration. 

 Real water plants respire with a lesser intensity than land plants, as Bohm^ 

 found in his experiments, by measuring in a hydrogen atmosphere the car- 

 bon dioxid given ofif during internal combustion. Since it may be assumed 

 that the amount of respiration is determined by the amount of protein 

 burned in the plant's body, the oxygen needed by the root system will be 

 greatest in cultivated plants, rich in nitrogen, and the most suitable soils 

 will be those which most completely satisfy this need together with the 

 other demands of the plant, i. e., rich field soil, which is loose or has been 

 loosened. 



Those lands, therefore, which are repeatedly subjected to an oxygen 

 scarcity, through the formation of crusts from rain action and the deposition 

 of silt by floods, will have to be improved by corresponding changes in their 

 physical structure. In the cases of souring, on the other hand, in which the 

 air supply is not necessarily cut ofif by the physical constitution of the soil 

 and in which only an excessive supply of water can fill the large interstices 

 in the soil, we will have to turn to the removal of the water.. Here deep 

 drainage or at least drainage canals 120 cm. deep, lowering the ground 

 water level by this amount, are the most advisable precautionary regulations. 

 The development of so deep a pervious layer is necessary because many 

 Leguminoseae, like alfalfa, and sainfoin, with their deep growing main 

 roots and fewer fibrous roots, are apt to die when they reach the ground 

 water. 



Souring of Potted Plants. 



The souring of potted plants occurs chiefly when loamy or peaty soils 

 are used. If the drainage hole of the flower pot is stopped up and excessive 

 amounts of water given by some inexperienced laborer, the roots of the 

 potted plants die completely, since they become brown and soft. 



The sour soil can be recognized at once by its characteristic odor. In 

 this the process of decomposition of the abundantly present organic frag- 

 ments, always contained in nutritive pot soils, takes place very differently. 

 Probably acid compounds and also free acids are produced from the but 

 imperfectly understood humus elements. If iron is present in the soil the 

 uninjurious ferric salts can be reduced to the injurious ferrous ones, since, 

 when the soil spaces are enlarged with water, a perceptible scarcity of 

 oxygen must occur. 



The water is saturated with carbon dioxid from the secretions of the 

 roots and also from the decomposition of the organic matters in the soil, 

 and, with continued action, the carbon dioxid is sufficient to kill the plants. 

 W. Wolf- proved experimentally that healthy plants, set in water contain- 

 ing carbon dioxid, at once began to eliminate it in very greatly reduced 

 quantities. The result is a wilting of the leaves which die later. 



1 Bohm, Ueber die Respiration von Wasserpflanzen, Sitzungsber d. Kais. Akad. 

 d. Wiss. zu Wien. 1S75, May Number. 



2 Tagebl. d. Naturf. Vers, zu Leipzig 1872, p. 209. 



