EXPERIMENT STATION REPORT. 363 



Internal troubles may be increased by external influences and 

 vice versa. As the ijradual chano-e of the new foliao'e of the 

 affected trees from a bright green to a white or bleached ap- 

 pearance, had to be ascribed to a suppressed formation of 

 the chlorophyl, my attention was quite naturally directed to 

 earlier observations of a similar character. Some experi- 

 ments by Nobbe, Schroeder andErdmann (Chemnitz, 1871), 

 had demonstrated the fact that the formation of the chloro- 

 phyl — the substance causing the green color of the plants — 

 could be controlled by the application of certain forms of 

 potassa, engaged my particular interest. Their observations 

 were made on rye and buckwheat. They had raised both 

 kinds of plants under well-defined circumstances, supplying 

 to one set the potash in the form of sulphate of potassium, 

 and the other in the form of chloride of potassium (muriate 

 of potash). 



The plants raised with the aid of the chloride of potassium 

 were of a vigorous growth, with a rich dark-green colored 

 foliage, and yielded a good crop of grain. Those raised by 

 the aid of the sulphate of potassa turned prematurely yellow 

 and failed gradually. 



An examination of the diseased lots of plants showed an 

 excessive accumulation of starch in the cellular tissue, whilst 

 but little chlorophyl was noticed. On the strength of these 

 considerations, I began a systematic investigation of the dis- 

 ease by an analytical chemical examination of various parts 

 of the peach tree in different stages of growth. The results 

 of these analyses are stated below in chronological order. 



A limited number of trees affected by the j^ellows were 

 also selected for the experiment with special manures. The 

 ground around the trees was treated with superphosphates 

 deficient in nitrogen (acid rock phosphate or soluble bone- 

 black) , and each tree (about eight years old ) received from 

 two to three pounds of muriate of potash, which was sown 

 broadcast over a surface extending about eight feet from the 

 trunk of the tree. None of these chemicals were brought 

 into close contact with the trees, except when spread over a 

 heavy mulch, to prevent serious reactions on the roots. The 

 diseased branches were cut back at the same time to the 

 healthy wood. 



