Jan. 6,1933 
A Phytophthora Footrot of Rhubarb 
11 
zinc stain, described by Stevens (^5, p. 300) and other authors. The 
figures in Plate 10, E, G, and H, are photomicrographs of typical spo¬ 
rangia before the escape of zoospores. These figures bring out clearly 
the apical papillae. Figures C and I in Plate 8 are catnera-lucida draw¬ 
ings of typical sporangia. 
Chlamydospores are sometimes very abundant in pure culture. They 
are spherical, thick-walled as compared with sporangia, and in some 
media slightly brownish in color. They, too, may be either terminal on 
the ends of short branches or intercalary. They are relatively large, 
measuring from 27 to 39 in diameter, 33 jjl being the mode, as indicated 
by Figure 2, depicting the results of 200 measurements. Plate 10, F, is 
a small, laterally attached chlamydospore, and Plate 8, A, one that is 
intercalary. 
Oospores are also found abundantly in pure culture, especially in some 
of the more nutrient media, such as oatmeal or lima bean agar, though 
they have been observed very thickly at times in corn meal agar, in the 
small piece of the medium with which the transfer was made from one 
tube to another. Oospores are spherical, ranging from 21 to 27 /z in dia¬ 
meter, the mode being 24 /z (fig. 2) and the mean a fraction less than 25 /z. 
The type of fertilization of the oogonium is always amphiginal, as de¬ 
scribed originally by Pethybridge (18, p. 536) and shortly after by Dastur 
