312 Wisconsin State Horticultural Society. 



sweepings and iron containing phosphates. The entire orchard 

 has received since, annually, some potash containing phosphates, 

 with good results. The special treatment of the diseased peach 

 trees, pronounced by good authority to be suffering from the yel- 

 lows, began in 1878, when my personal attention was first called 

 to its appearance on the top of the knoll in the college orchard. 

 The general appearance of the diseased trees suggested to my 

 mind, at first, that an abnormal condition of the soil might be the 

 cause. Tbis condition might be ascribed either to a more or les& 

 general exhaustion, or to an absence of only some one or other 

 essential element of plant food ; or, finally, to the presence of some 

 in]uri()us substances which might have accumulated in the soil 

 from some cause or other in the course of time. I felt inclined to' 

 consider, in either of these cases, the fungus which covers and 

 disfigures the diseased parts of the trees a secondary feature of 

 the disease. My observations of later years, with grape vines 

 and currants in particular, have lended to strengthen in my mind 

 that view in regard to many of our troubles with parasitic growth 

 and diseases of plants. I have repeatedly noticed that plants suf- 

 fered seriously from mildew and blight upon unfertilized and ex- 

 hausted lands, when upon adjoining fertilized plats no sign could 

 be noticed. On the other hand, the healthy condition of the 

 roots, even to the last stage of the disease, and also the gradual 

 disappearance of the green color, indicating insufficient production 

 of chlorophyll, which causes the gradual change from a healthy 

 appearance to a sickly one, beginning with the outer termination 

 of the branches, which is the most active part for the formation of 

 new vegetable matter, seemed to point towards a localized trouble, 

 — a possible interference with the normal cellular functions, — 

 an alteration of the osmotic action of the cellular tissues, and thus 

 subsequent death of its affected part. This view of the case 

 found support in the well known observations of Messrs. ISTobbe, 

 Schioeder, and Erdmann, regarding the action of sulphate of 

 potassa and chloride of potassium on the growing of rye and of 

 buckwheat. Sulphate of potassa had caused first a premature yel- 

 low color of the entire plant, which terminated with its gradual fail- 

 ing; whilst the chloride of potassium (muriate of potash) had 



