Methods in Rust Investigations 255 



While detailed notes are necessary when an investigation is in pro- 

 gress, they would only be confusing in a publication of I'esults. At this 

 stage, however, the various types of susceptibility can be placed in a 

 relatively few classes with some degree of accuracy. Vavilow (1913) fol- 

 lowing Eriksson has employed a classification based largely on the 

 amount of uredinia developed on grain in the field. Stakman and Le- 

 vme (1922) and a number of other investigators have used a similar 

 system for their greenhouse investigations of Puccinia graminis, symp- 

 toms as well as quantity of uredinia being used as criteria. Mains and 

 Leighty (1923) have used a similar classification for Puccinia dispersa. 

 This may be arranged as follows for the leaf rusts of wheat and rye: 



0. No uredinia formed; hypersensitive areas sometimes present 

 and definite, sometimes faint or absent. Fig. 5, I. 



1. Uredinia few, minute, in the center of definite hypersensitive 

 areas; few to many hypersensitive areas without uredinia. Fig. .5, H, G. 



2. Uredinia fairly abundant, moderate in size but always sur- 

 rounded by hypersensitive areas, hypersensitive areas seldom without 

 uredinia. Fig. 5, F. 



3. Uredinia abundant, moderate in size, without hypersensitive 

 areas but in some cases surrounded by slightly chlorotic tissue. Fig. 

 5, C, B. 



4. Uredinia abundant, very large, hypersensitiveness absent but 

 uredinia occasionally in green islands. Fig. 5, D. 



Where time is available, perhaps the best method of taking notes 

 is to make herbarium specimens, especially where there is likely to be 

 need of critical comparison later on. If infected leaves are dried quickly 

 under moderate pressure, they will lose very little in color or other 

 characters and will serve foi- several years at least as good material 

 for reference. The plant press desci-ibed by Jackson (1921) has been 

 found especially good for this purpose, as the drying is very rapid, 12 

 hours usually being sufficient. 



Photographs also are very important records, especially when pub- 

 lishing results. Many of the rusts are very difficult to photograph. 

 This is especially true in the case of Puccinia triticina, where the ure- 

 dinia are orange and the leaf is green in color. By the use of Wratten 

 & Wainwright panchromatic plates and the B (green) Wratten M filter 

 and enlarging two or three times, the uredinia photograph very well. 

 Where a number of diff"erent types of susceptibility are to be photo- 

 graphed together, filters usually cut down the contrast on some of the 

 types. It has been found that photographing by both reflected and 

 transmitted light shows practically all the characters well defined, the 

 uredinia appearing darker on account of transmitting less light than 

 the leaf and the chlorotic areas, necrotic areas, and flecks appear lighter 

 because they transmit more light. 



Literature Cited. 



Carleton, M. A. Culture Methods with Uredineae. Jour. Applied 

 Micros, and Lab. Methods. 6: 2109-2114. 1903. 



