BIOLOGIC SPECIALIZATION IN THE GENUS SEPTORIA 
5 
Experimental Methods and Material 
The species of Septoria for investigation were with few exceptions col- 
lected in the vicinity of Urbana, Illinois. During the growing season spore- 
bearing material was gathered in the field from naturally infected plants. 
In fall and winter spores were obtained in most cases from pure cultures 
isolated before the first frost. In preparation for inoculation, spore sus- 
pensions were made with distilled water and were concentrated enough to 
contain fifty to one hundred spores per loop. 
The experiments were begun in June and were continued to the fol- 
lowing April. In summer the work was conducted in the field upon plants 
growing in their natural state. Freedom from disturbance and as far as 
possible from natural infection governed the selection of suitable individuals. 
After the first frost the experiments were continued in the greenhouse upon 
potted plants transplanted from nature or grown from seed. 
The method of inoculation was somewhat varied. In the field an 
atomizer was most convenient, for the spore suspension could be carried 
safely in the glass container. In the greenhouse a wire loop was more 
commonly used to spread drops of the suspension over the leaf surface. 
Where a bloom or other epidermal structures made it difficult to secure 
good contact, especially with leaves of grasses, the suspension was rubbed 
on with the clean finger tips with proper care. Consistency of method was 
followed in a single series to secure comparable results. The entire surface 
of certain leaves was inoculated, while adjacent leaves of the same plant or 
of near-by plants were used as checks to detect foreign infection where there 
was danger of this. Inoculations were made upon individuals of the original 
host to afford a check upon the viability of spores, or upon unfavorable 
environmental conditions. 
In providing conditions favorable for infection, covers made of paraffined 
paper bags were found to give the most satisfactory results. Some use 
was also made of bell jars. The inoculated leaves, or the entire plant, 
were covered for periods varying from three to five days. In cases in which 
disease spots without pycnidia resulted, the bags were replaced over the 
plants for a second period to promote the growth of the fungus, and to 
induce if possible the development of spore-bearing bodies. If this failed, 
the spotted leaves were detached and put into a sterile moist chamber. 
In this manner pycnidia were obtained and infection proved in some cases 
in which results would otherwise have been in doubt. This was especially 
necessary in instances in which spore suspensions were made from natural 
material, and the spores of other fungi might have been present to cause 
the spots. 
In the following accounts the results of the inter-inoculations with each 
species of Septoria are presented graphically by means of diagrams, and 
in more detail in a few representative cases by means of tables. The arrows 
in the diagrams indicate infection, and the lines ending in bars non-infection. 
