142 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



despite the best efforts in spraying, lost from 10 to 25 per cent each 

 year. Adjacent orchards during the year lost about 50 per cent on 

 early varieties and 25 per cent on late varieties. 



Peach and plum spot. — The bacterial spot on peach and plum has 

 not proved amenable to spray treatment. Experiments in control- 

 ling this disease by means of nitrate of soda applied to the soil were 

 tried out on a large scale with complete success. The life history 

 of the organism causing this disease is being studied. 



Stigmonose of fruits. — The work of the present year has given 

 further confirmation of the previous year's experiments and estab- 

 lished the connection of certain insects with particular types of fruit 

 spotting. Experiments on rosy aphis stigmonose have been carried 

 out at Staunton, Va., and similar work has been carried on in co- 

 operation with the Bureau of Entomology at Wenatchee, Wash. 

 The work in Virginia has shown conclusively that much of the so- 

 called "York" spot of the Eastern States is stigmonose due to insects. 

 This type of disease is, therefore, capable of control by spraying 

 methods developed by the Bureau of Entomology. Experiments 

 have been made in the control of this disease, and the first year's 

 results of spraying show that the fruit from sprayed plats will stand 

 up in shipment far better than the fruit from unsprayed plats. 



PLANT PHYSIOLOGICAL INVESTIGATIONS. 



Clover-sick soils. — Experiments in clover-sick regions are now 

 being started in cooperation with the Indiana experiment station 

 and with the Winconsin experiment station. The results so far 

 obtained indicate that with the incorporation of certain green ma- 

 nures, together with the proper fertilizer treatment, clover sickness 

 can be controlled or sufficiently overcome to make clover growing 

 again profitable in these regions. 



New soil compounds. — The fundamental investigations into the 

 nature of organic soil constituents and the chemistry of humus in 

 general have progressed, and in the course of the year several definite 

 organic acids which throw light on the decay of organic matter of 

 soils have been isolated. An especially interesting acid with pe- 

 culiar properties has been isolated from a very unproductive soil 

 and recommendations for its elimination under field conditions made 

 as a result of our studies. An organic colloid of complex carbohy- 

 drate nature which has a marked influence on physical and bio- 

 chemical properties of the soil has been isolated and studied. The 

 field studies on the action of harmful soil constituents have been 

 continued under different soil and climatic conditions at the Arling- 

 ton Farm, Pennsylvania Agricultural Experiment Station, and the 

 Cornell Agricultural Experiment Station. In different soils these 

 compounds exhibit a different intensity of action, which is shown 

 to be due to a partial or complete destruction of the compound 

 under the existing soil conditions. The influence of fertilizers on 

 different compounds as they exist in soils is practically found to be 

 specific, and this fact is being utilized in conducting field demon- 

 strations to free the soil from these compounds where they have been 

 encountered. 



