242 
Journal of Agricultural Research 
Vol. VIII, No. 7 
of withstanding adverse conditions than the ordinary hvphae. These 
protuberances on the mycelium of P. syringae grown on potato agar can 
be used to advantage in separating it from the other species. It is prac¬ 
tically impossible to distinguish any of the other species by their mycelial 
characters with any degree of accuracy. It should be noted* however, 
that the mycelium of P. nicotianae , whether grown on oat or potato agar, 
generally contains larger and a greater number of the globoid particles 
of a fatty or glycogen nature than any of the other species. 
The size of the mycelia varies greatly, as shown by measurements 
made from aerial and from submerged growth. The following are the 
limits of variation for each of the different forms: 
FORM. 
P. parasitica 
P. infestans ..... 
P. phaseoli . 
P. syringae . 
P. nicotianae ..., 
P. jatrophae . 
P. arecae . 
P. cactorum . 
P. faberi . 
P. fagi . 
P. erythroseptica , 
size. 
M 
1. 91 to 7. 66 
2. 87 to 11. 49 
2. 87 to 11. 49 
2. 87 to 7. 66 
2. 87 to 17. 23 
1. 27 to 7. 66 
1. 91 to 7. 66 
1. 91 to 7. 66 
1. 91 to 7. 66 
1. 91 to 7. 66 
1. 91 to 7. 66 
CONIDIOPHORES 
As several of the forms produced very few or no conidia-bearing 
hyphae on the ordinary agars previously employed, it was necessary to 
grow some of them on special media in order to study the conidiophores. 
For example, in the case of P. erythroseptica , it was necessary to use 
flies as the medium in order to obtain conidiophores. Owing to the great 
length of these structures and the manner in which spores are borne, they 
can not be studied under high magnification. 
The general procedure followed varied according to the form. By 
means of the following method the majority were easily studied: Van 
Tieghem cells were carefully cleansed and placed in a large moist chamber 
and sterilized. Clean cover glasses were flamed, and a drop or two of 
melted media placed on each and allowed to harden, at the same time 
all possible precautions being taken to prevent contamination. After this 
each drop was inoculated with a pure culture of the form to be studied, 
and the cover glasses then inverted on the Van Tieghem cells, at the 
bottom of which a few drops of sterile water had previously been placed. 
The cover glasses were held in place by means of sterilized vaseline. At 
the end of not less than 36 hours the conidiophores and conidia began to 
appear and were easily examined with the low magnification of the 
microscope. 
