406 FUNGOUS DISEASES OF PLANTS 



with four germ pores. They measure 21-24/1. They are produced 

 in such abundance as to be dusted in quantity upon any passing 

 object or taken in clouds by the wind for some distance. They 

 are unquestionably the chief means of distributing the disease 

 during the growing season. It has been found (Smith) that their 

 vitality upon drying is not retained for more than a few months. 



The black rust stage appears later in the season, apparently as- 

 the conditions for uredosporic formation become unfavorable. The 

 sori are black-brown, and while for a time protected by the epi- 

 dermis, they are finally exposed. The teleutospores are elliptical, 

 slightly constricted, as a rule, and measure 30-60 x 21-28 /x. The 

 wall is thick at the apex, and the pedicels very long. These spores 

 show a more or less persistent attachment to the host. Unicellular 

 teleutospores also occur. They have been germinated towards the 

 middle or end of winter, with the characteristic promycelium and 

 sporidia. It is believed that the general infection in cultivated 

 fields each season results from aecidiospores produced on wild or 

 escaped plants, and not directly from the germination of teleuto- 

 spores which have remained in or about the soil. 



Control. The numerous attempts which have been made to 

 control the asparagus rust by means of Bordeaux mixture have 

 been more or less unsuccessful. Nevertheless, Sirrine, in experi- 

 ments on Long Island, and later others have used to advantage 

 a Bordeaux prepared with resin. The mixture which may be 

 recommended is as follows : 



Bordeaux mixture, 5-5-40 formula, 40 gals. 

 Resin mixture, 2 gals., diluted to 10 gals. 



The resin preparation consists of resin, 5 Ibs. ; potash lye, I Ib. ; fish oil, i pt. ; 

 and water, 5 gals. 



In California it has been found that under certain climatic con- 

 ditions thorough spraying with sulfur, either as dust or liquid, is 

 an efficient preventive, the prevention resulting from the fumes. 

 In any case, however, where control' consists in the use of sprays, 

 provision should be made for the best circulation of air possible, 

 that is, the field should be as free from obstructions around the 

 border, and the rows should be a sufficient distance apart so as 

 not to make the conditions any more favorable than possible for 

 high moisture content of the air. Thorough cultivation should be 



