14 TECHNICAL BULLETIN 17 



TABLE IV 



SUMMARY OF COMPARISONS BETWEEN MEANS AND COEFFICIENTS OF VARIABILITY FOR LENGTH o* 



SPORES OF Helminthosporium sativum PRODUCED UNDER DIFFERENT CONDITIONS 



FROM DATA SUMMARIZED IN TABLE III. 



These facts show that in a single spore strain of a Helnuntho- 

 sporium of this type, marked variations may be found in the length 

 of spores developed under various conditions. Differences in spore 

 measurements by various authors are therefore to be expected, and 

 very fine specific or varietal differences can not be drawn on, the basis 

 of spore size unless a large number of carefully controlled compara- 

 tive studies have been made. Seemingly, the original spore meas- 

 urements given by Pammel, King and Bakke are rather large (105 

 to 130 microns). Stevens has come nearest to approaching this length 

 with a maximum of 122 microns. The same author states that the 

 majority of his spores fall within 80 to 90 microns. By examining 

 Table III it will be seen that the majority of the spores developed 

 upon fresh barley leaves in a moist atmosphere fall within the 80 and 

 90 classes, or within 75.0 to 94.9 microns. Out of 4000 spores meas- 

 ured, only 43. were longer than 100 microns. On the fresh leaves the 

 longest spore measured was only 115.5 microns. However, the opti- 

 mum conditions for maximum and minimum spore length have not 



