284 
Journal of Agricultural Research 
Vol. XXX, No. 3 
Greenhouse series .—A selection of 10 
specimens of each species from collec¬ 
tions made in the pathological green¬ 
houses at Washington, D. C., one 
specimen of each species in each set; 
set numbers 21-30, inclusive. 
placed in a small drop of the following 
medium: 5 
Potassium acetate....10 gms. 
Distilled water...... 500 cc. 
Pure glycerine__ 200 cc. 
Ethyl alcohol, 95 per cent_ 300 cc. 
Erythrosin----10 gms. 
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Fig. 1.—Graphs showing the length and width means for 30 sets of urediniospores of Cronartium ribicola 
and Cronartium occidentale. Each point on each species line represents the mean of 100 measurements. 
The series are explained in the text. The set numbers correspond to those in the last columns of Tables 
I to IV 
The collection data are given in full 
in Tables I to IV. 
MOUNTING 
The spores were removed from the 
uredinia as carefully as possible and 
They were left in this medium with¬ 
out being covered with a cover glass 
for several hours. The mount was then 
finished by adding a drop of glycerine 
jelly made up as follows: 
Fig. 2.— Graphs showing the mean wall thickness for 30 sets of urediniospores of Cronartium ribicola and 
Cronartium occidentale. Each point on each species line represents the mean of 50 measurements. Series 
and set numbers as in Figure 1 % ____ 
* This medium has been used for years in the Bureau of Plant Industry by Dr C. L. Shear and others. 
The only modification of their formula is the addition of the erythrosin. 
