250 
Journal of Agricultural Research 
Vol. VIII, No. 7 
them quantitatively. The writer proposes the following method for 
this purpose: 
The differences ranging from ellipsoidal to spherical may be expressed 
largely as differences between the ratios of the length of the two diame¬ 
ters drawn perpendicular to each other. Thus, in text figure 7 is shown 
an extreme case of two forms, one ellipsoidal and the other spherical. 
The difference between these may be indicated by the difference between 
and and expressed quantitatively 2 and 1, since in this hypo¬ 
thetical case aa is twice the length of bb , and bb is equal to a f a f and b 
Fig. 4.—Oraph showing the variation in width of conidia of Phytophlhora 
fagi, P. phaseoli, P. faberi, and P. jatrophae. 
As previously stated, the conidia of the Phytophlhora spp. vary from 
elliptical to globose; therefore measurements made of each conidium of 
the long and short diameters, as shown above, will express quantitatively 
the difference heretofore expressed qualitatively. Such measurements in 
microns were made from conidia of each species taken at random from 
normal culture. Four hundred conidia were measured for each species 
and the ratio of the long and the short diameter of each determined. 
Figure 8 shows diagrammatically the classification of these ratios. It also 
shows the predominating ratio in each form, as well as the maximum 
and minimum limits. From this it will be seen at a glance that the 
