19 



of all the pots bj' means of heat and to reinoculate them by means of 

 a small portion of soil selected from a field which might reasonablj^ 

 be presumed to be free from the fungus whicli had caused the trouble. 

 This reinoculation was of course necessary to renew within the soils 

 those forms of lower plant life which are helpful to the growing plants. 



A plan was finally devised by which this sterilization and inocula- 

 tion could be carried out, although the treatment of 177 portions of 

 soil b}' these processes was a very laborious task. Three dozen covered 

 sheet-iron pans were obtained, of such size that each pan would hold 

 the soil contained in one pot. The soils contained in these pans were 

 subjected to heat on eacli of three successive days, the temperature 

 being carried approximately to 100° C. during the course of each heat- 

 ing. The soils were kept as moist as possible during the process, inas- 

 much as sterilization by heating is more effective when the material to 

 be sterilized is kept moist. A large drjdngoven, already in use in the 

 laboratory for other purposes, was found very convenient for heating 

 the pans of soil during the sterilization, as the oven is of such a size 

 as to accommodate from ten to twelve pans at one time. The pots 

 were also sterilized l\v washing, steaming, dipping in bichlorid of 

 mercury solution, and then thoroughly washing. The soils contained 

 in the pans, after sterilization, were mixed with 100 grams of the soil 

 used as the inoculating material preparatory to being returned to the 

 pots. 



While the growth of the plants during the present season shows 

 that tlie destructive work of this fungus has been practically' elimi- 

 nated, there is abundant evidence that several causes contributed to 

 the poor growth of the bean plants in several of the pots. The cause 

 or combination of causes is yet somewhat obscure, but the experience 

 of this season gives several clues to the means of ultimately overcom- 

 ing this difficulty. The growth of the oats in the pots planted in 

 that crop has been very satisfactory. 



STUDY OF SOIL BACTERIA USEFUL OR HURTFUL IN AGRICULTURE. 



Since the discovery of the nitrifying organisms b3^ Schloessing and 

 Miintz in 1877, the attention of agricultural scientists has been directed 

 to the study of those organisms in the soil which are either helpful or 

 harmful to the higher forms of plant life. There has been developed 

 an immense literature on the subject, which, however, is now scattered 

 through a great number of monographs and scientific periodicals of 

 recent date. There is no exhaustive treatise in any language which 

 reviews the entire subject and treats of the agricultural importance of 

 these organisms, including the best methods of enabling the farmers 

 to derive the greatest amount of benefit from the useful ones and to 

 reduce the activity of the harmful ones to a minimum. It has been 

 my purpose, since the authorization was given me and the necessary 

 appropriations first provided in 1894, to compile this information in 

 such a form that it would be useful to the American farmer as well 

 as to our very large corps of scientific investigators. 



I have also endeavored, by means of investigations in the labora- 

 tor3^ to add to our knowledge of these organisms and their relations 

 to agricultural operations. A considerable amount of time has already 

 been devoted to the subject, and the systematic review of the literature 

 bearing upon it is now nearing completion. It is hoped that that part 

 of the work having reference particularly to the nitrifying organisms 

 may be ready for the printer within a few months. 



