Feb. 12,1917 
Studies of the Genus Phytophthora 
243 
The number of conidia found on a single conidiophore varies from a 
minimum of 2 to a maximum of more than 20. The sympodial type of 
branching prevails. Plate 72 shows representative types of conidiophores 
in the various forms made with the 7.5 ocular and 16 mm. objective. As 
shown in this plate, such forms as P. phaseoli and P. nicotianae are more 
prolific in the production of conidia than others. Examination of the 
conidiophores of P. infestans y P. phaseoli , and P. thalictri with a higher 
magnification showed that they differ from the other forms in that there is 
a slight thickening 
of the conidio¬ 
phore immediately 
below the point 
of attachment. 
This character is 
constant on both 
the natural sub¬ 
stratum andin the 
artificial cultures, 
as shown by both 
P. infestans and 
P. phaseoli . The 
conidiophores 
vary greatly in 
size, the variation 
ranging from 200 
to 500 m in length 
and 3.5 to 8.5 Min 
width. 
CONIDIA 
Conidia are 
formed in all the 
species of Phy¬ 
tophthora studied, 
and are almost 
always terminal, 
although in rare 
instances structures are seen which may be intercalary conidia. They are 
elliptical to ovate, approaching the globose, with a more or less prominent 
apical papillum. In all the forms the color of the conidia is the same—that 
is, pale gray to colorless. The contents in all cases are finely granular, some¬ 
times with a large central vacuole. The size of the granules and the pres¬ 
ence of vacuoles depend on the age of the conidium. As it advances in 
age the protoplasm and granules appear to divide and become less dense 
and the number of vacuoles may also increase. Neither the color nor 
infestans, P.fagi, P. parasitica, and P. jatrophae. 
