1919] SOILS FERTILIZERS. 217 



reduction of the toxic property to seed germination and plant growtli by 

 the activity of soil flora has been demonstrated, and is held to be contrary 

 to Pickering's conclusion that loss of toxicity in storage of heated soils is 

 an oxidation process which may go on under aseptic conditions (E. S. R., 24, 

 pp. 420, 421). 



Tlie beneficial action of highly heated soils is believed to be due largely 

 to the ammonia liberated on heating, since increased growth may result in 

 almost total absence of nitrates or in heated soil under aseptic conditions in 

 spite of a considerable toxic action upon the roots. That certain green plants 

 are capable of utilizing nitrogen in the form of ammonia is believed partially 

 to explain the variation of sensitiveness of plants to heated soils. The 

 temperature of the soil was shown to be an Important factor in determin- 

 ing the extent of the toxic and beneficial action to plant growth, the toxic 

 .action disappearing more slowly and being more destructive at low soil tem- 

 peratures (below about 25°) than at higher temperatures. 



Observations on the growth of Pyronema are held to indicate that the 

 favorableness of heated soils to its growth is not entirely one of concentra- 

 tion of soil solution, as argued by Seaver and Clark (E. S. R., 23, p. 629; 27, 

 p. 620), since Pyronema grew on heated soils very low in concentration as 

 compared with other unheated soils on which growth never occurred. All 

 microorganisms appeared to grow better on soils having a high concentra- 

 tion of soil solution due to increased food supply, but the type of organism 

 and the extent of its growth varied with the competition at hand and the 

 kind of food materials present. Fungi differed in their food requirements in 

 much the same way as green plants, and heating the soil is thought to pro- 

 duce chemical substances specially favorable to the growth of Pyronema. 



The conclusions reached are deemed applicable particularly to highly heated 

 Boils, although it is not believed that any fundamental difference exists between 

 ordinary steam-sterilized soils and highly heated soils reinoculated with normal- 

 soil flora. " Although the injurious action of heated soils on plant growth has 

 been brought into the foreground in this paper, it is not desired to leave the 

 impression that heat-sterilized soils are of questionable value in research and 

 practice. The opposite is rather true, and little hesitancy need be felt in 

 recommending steam sterilization of soil for practical purposes or for use in 

 research problems where it is necessary to eliminate certain organisms from 

 the soil. But one must be prepared to expect a short period of retardation of 

 growth, followed by a beneficial action, and in special cases, with certain soils 

 or plants or under certain environmental conditions, a very marked interference 

 vnth the normal development of plants." 



A list of references comprising 79 titles is appended. 



The actinomyces of the soil, S. A. Waksman and R. E. Curtis {Soil Sci., 

 1 (1016), No. 2, pp. 99-134, pis. 3, fig. 1). — In this paper, a contribution from the 

 New Jersey Experiment Stations, the authors demonstrate the presence of Acti- 

 nomycetes in different types of soil and attempt a classification of the organ- 

 isms according to their morphological and physiological characters. More than 

 100 organisms were isolated, representing 30 species which are described and 

 a key prepared for their identification. A list of references comprising 23 titles 

 is appended. 



The occurrence of Actinomycetes in the soil, S. A. Waksman and R. E. 

 Curtis {Soil Sci., 6 {1918), No. J,, pp. 309-3i9).— Supplementing the work noted 

 above, information is given concerning the number of Actinomycetes and bac- 

 teria occurring in 25 soils from different sections of North America and from 

 the Hawaiian Islands previously described (E. S. R., 36, p. 214), together with 



