DISEASES OF PLANTS. 225 



the iiioeuliitioii except where the rust was taken from the same kind 

 of host upoji which it was inoculated. Plants of oats, wheat, rye, and 

 orchard grass were inoculated in October with uredospores of P. 

 graminis from oats. Of these only the oats were infected. At the 

 same time another series of plants was inoculated with the uredo- 

 spores of P. riihigo-vera from wheat, aud only the wheat plants were 

 infected. In all cases where infection resulted the period of incubation 

 was about lo days. 



• These experiments seem to show that there is little danger of infec- 

 tion from one kind of grain to another. 



Spraying experiments were made to determine what chemicals would 

 prevent rust when applied in solutions of such strength as to avoid 

 injury to the plant when sprayed. The compounds of the following 

 were used in solutions of various strengths: Potassium bichromate, 

 mercuric chlorid, copper sulphate, copper acetate, copj)er nitrate, lead 

 acetate, copper chlorid, ferric chlorid, zinc chlorid, and ferrous sul- 

 l^hate. To these fungicides were afterwards added common salt and 

 boric acid. 



Tabulated information is given as to the varieties of wheat experi- 

 mented upon, strength of solution, and effect of the fungicide upon the 

 plant. 



The sxjrayiug was not begun until 3 days after the rust began to 

 appear, and it ran its course so rapidly that time was given for but one 

 spraying. At the same time P. (jraminis began to appear upon the 

 oat crop, and the same fungicides, with the exception of copper chlorid, 

 copper acetate, and zinc chlorid, were tested upon the oats. 



The two requisites found necessary for the successful spraying of 

 rusts seem to be (1) to obtain a solution of sufticient strength to effect- 

 ually combat the rust without injury to the plant, and (2) to find some 

 method of covering the plants more completely with the spray. The 

 former requisite the authors consider as practically within their reach. 



On June 28, specimens of the plants were taken from the treated plats 

 and compared as to the amount of rust with specimens from untreate I 

 portions. Taking the average amount of rust on the untreated portions 

 as 100 per cent, the amounts on the lilats treated with the different 

 fungicides were approximately as follows : Salt, 100 per cent; boric acid, 

 85; ferrous sulphate, 85; lead acetate, 85; copper sulphate, 50; copper 

 nitrate, 25; mercuric chlorid, 25; potassium bichromate, 10; and ferric 

 chlorid, 10. 



The authors' conclusions are as follows: 



"(1) lu the vicinity of Manhattan, the common wheat rust, Puccxnia ruhigo-vera, 

 passes the winter in the tissues of the wheat plant in the mycelial condition. During 

 the warm weather of spring a crop of spores is iiroduced which under favorable condi- 

 tions may rapidly spread the disease. The infection of the winter wheat in the fall is 

 materially aided by volunteer wheat, which carries the rust through the few months 

 following harvest. The red rust spores are capable of maintaining their power of 

 germination through the winter and thus infecting the crop the following spring. 



