﻿Exposure and fungous Diseases.* 



By Byron D. Halsted. 



Exposure has something to do with the attack of parasitic 

 fungi and this may be of at least two kinds — to the elements 

 sunshine, air, moisture, etc., and to the germs of the disease. Both 

 of these sets of conditions work together for the production of in- 

 fection. 



Some striking illustrations of the value of exposure to the 

 germs in the success of inoculation have come under the writer's 

 notice within the past year. Attention is directed to the infestation 

 of a young growth of asparagus to the rust fungus, Puccima as- 

 paragi DC. On September sixth, while inspecting asparagus 

 fields in Gloucester county, New Jersey, the writer came to a field 

 with quite an unusual green appearance, nearly all the fields being 

 brown and lifeless so far as the brush was concerned, having been 

 killed by the remarkable ravages of the rust fungus. The field in 

 question had been cut over and the very rusty brush removed 

 about five weeks before, with the hope that the new growth might 

 escape the ravages of the Puccima. At the date of the inspection 

 the brush was about hip high and showing the rust only upon 

 one side of each plant So strikingly one-sided was the out- 

 put of the rust sori that one could scarcely fail to observe it. 

 Every main stem was almost completely covered with the rust 

 upon one side, while the opposite bore almost no spots. It was also 

 noticed that this rusted side varied somewhat at different ends of 

 the long field, and at all points was at right angles to lines drawn 

 from an old and very badly rusted bed of asparagus that stood 

 with its end towards the broad side of the field in question and 

 about forty rods away. 



This observation teaches something concerning the rapidity ot 

 the development of the rust fungus. As the brush must needs 

 have been developed to some extent before the uredospores could 

 have alighted upon them, and as also it is fair to judge that many 



* 



Prepared for the Botanical Club of the A. A. A. S., Boston, Mass 



(622) 



