PLANT GROWTH. 441 



In the case of pear trees in different plats, which were 

 treated in the same way and at the same time with both fer- 

 tilizers, Fertilizer No. 1 has produced the best results in 

 growth and in fruit. Both, however, surpass the unfertilized 

 trees. 



In 1880 a new series of experiments was inaugurated with 

 iron 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 yellows, began in 1878, when my personal 

 attention was first called to its appearance on the top of the 

 knoll in the colleo;e orchard. Instead of undertakins: to 

 describe here the characteristics of that much-dreaded dis- 

 ease of the peach tree, I prefer to leave that task to my 

 friend. Professor D. P. Penhallow, a graduate of the Massa- 

 chusetts Agricultural College in 1873, who has kindly as- 

 sisted us during the past eight months by carrying on such 

 microscopic observations, regarding the origin and the 

 nature of the disease through some of its various stages, as 

 seemed desirable to me for the formation of an intellio;ent 

 opinion concerning the possible cause of the disease. The 

 results of Professor Penhallow's work are of unusual inter- 

 est, and I do not doubt will be deservedly appreciated by all 

 those who take an interest in the subject here under discus- 

 sion. The manuscript containing a detailed description of 

 the characteristics of the disease, and his microscopic work, 

 illustrated by drawings representing various stages of the 

 disease, will form a most valuable addition to the present 

 discourse. The manuscript is at the service of the society ; 

 and the Professor, who, at my solicitation, is present, will 

 be pleased to explain his observations if desired to do so. 



The general appearance of the diseased trees suggested to 

 my mind, at first, that an abnormal condition of the soil 

 might be the cause. This condition might be ascribed 

 either to a more or less general exhaustion, or to an absence 

 of only some one or other essential element of plant food ; 

 or, finally, to the presence of some injurious substances 

 which might have accumulated in the soil from some cause 

 or other in the course of time. I felt inclined to consider. 



