30 BULLETIN 380, U. S. DEPARTMENT OF AGRICULTURE, 



less irregular on account of crowding. This pressure may be so 

 great as to produce almost any shape, and such perithecia some- 

 times measure 0.5 mm. in the greatest diameter and 0.1 mm. in the 

 shortest. 



SPORE MEASUREMENTS. 



The spore measurements recorded here were made by Miss Tiller. 

 In the case of dried specimens, the spores were first soaked for three 

 hours in lukewarm water and then mounted in the potassium- 

 glycerine-copper medium, prepared according to the following 

 formula : 



1 part 2 per cent potassium acetate in water. 



1 part 40 per cent glycerine in alcohol. 



Copper acetate sufficient to color. 



In the case of fresh specimens they were mounted directly in the 

 same medium. The measurements were made with a Zeiss filar 

 ej^epiece micrometer and a Zeiss 3 mm. 1.40 N. Ap. oil-immersion 

 objective. Only approximate accuracy is claimed for these results, 

 on account of the difficulty of overcoming the motion of the spores 

 in a fluid medium. The results are, however, believed to be fairly 

 comparable, as practically all were measured under the same condi- 

 tions and treatment, and the margin of error is presumably rather 

 uniform. The differences in size of pycnospores do not appear to 

 be sufficient, however, to furnish diagnostic character for most of 

 the species. 



The number of measurements of ascospores of Endothia fluens and 

 E. parasitica is much larger than of the other species, as special 

 attention was first given to these two species on account of their great 

 similarity. In order to make the measurements of these species 

 comparable to the others, the total number of spores of each length 

 has been calculated in the percentage of the total number of spores 

 measured. 



METHOD OF TABULATION. 



For better comparison, the spore measurements have been tabu- 

 lated by half microns, all the spores in each specimen coming within 

 0.2 of a micron of each unit or half being grouped together; e. g., 

 all the spores having a length of 7.3, 7.4, 7.5, 7.6, and 7.7 microns 

 are included under the heading 7.5. The tables thus show at a 

 glance the number of spores of a given length per specimen. The 

 widths have been tabulated in the same way. 



For a better comparison of the shapes of the ascospores of 

 Endothia parasitica and E. fluens, the relative ratios of length to 

 width in each spore have been calculated, the width being considered 

 unity. The ratios of length to width were then tabulated by tenths; 

 that is, all the spores in each specimen having a ratio of length to 



