200 AGRICULTURAL EXPERIMENT STATION. [Jan. 



XII. Department of Vegetable Physiology. 



Report by Prof. James Ellis Humphrey. 



The past year has seen the department finally settled in 

 the new quarters provided for it, and fairl}^ equipped for 

 work. Owing to repeated delays, the new laboratory was 

 not occupied until the middle of March, and the green- 

 house was completed so late that it did not become practi- 

 cally available until fall. Therefore the present contains 

 no reports of greenhouse work. What has been done the 

 past fall consists of preparations for and the beginnings of 

 experiments not yet completed, and is reserved until results 

 can be reported. 



The work of the past year here reported upon consists 

 of laboratory and field studies of several diseases which 

 cause very severe losses to farmers and fruit growers, or of 

 the fungi which cause them, as follows : — 



1. The black knot of the plum. 



2. The mildew of cucumbers, etc. 



3. The brown rot of stone fruits. 



4. The potato scab. 



5. Notes on various diseases. 



Reference to the "General Account of the Fungi," in 

 the last report of this station, will be found of assistance to 

 a full comprehension of the following discussions. 



The Black Knot of the Plum. — Ploxvrightia 

 inorbosa (Schw.) Sacc. 



For a hundred years complaints have come from one or 

 another part of the United States of the destruction of 

 plum and cherry trees through the attacks of a conspic- 

 uous and fatal disease, which shows itself in the formation 

 of dark, rough excrescences upon the limbs or even on the 

 trunk of the tree. 



These growths increase both in size and in number, 

 spreading from branch to branch and trom tree to tree, in 

 a manner strongly suggesting their contagious nature ; and 



