BIOLOGIC SPECIALIZATION IN THE GENUS SEPTORIA 
13 
October the leaves in these clumps were badly attacked by Septoria. Col- 
lections for purposes of inoculation were made at this time, and also in 
December and January. After the ground froze the clumps were cut out, 
allowed to thaw slowly, and were then kept in a closed collecting can in the 
greenhouse. In a few days the pycnidia were forming spores abundantly. 
The spores from this source, collected either in summer or winter, were 
septate, and the pycnidia were brownish-black, round to elliptical when 
viewed from above, usually arranged in rows between the leaf veins, and 
were often visible to the naked eye. The spores from the leaves of the 
plants that had been frozen and then treated as mentioned were much longer 
but somewhat more slender than spores from material collected in other 
ways. Septation was difficult to detect and seemed to be absent in some 
cases, but proper staining made it apparent in most of the spores. The 
pycnidia under these same conditions were often more than double their 
ordinary size, but were unchanged in shape. Infections obtained upon 
wheat seedlings by inoculation with these longer types of spores always 
resulted in pycnidia of normal proportions, and in shorter spores with more 
definite septa, typical of the fungus found on the leaves of wheat in summer 
or fall. A more comprehensive description of these morphological varia- 
tions will be given in a subsequent section. 
Whether one base his conclusions upon Cavara's revised descriptions, 
or upon his assertion that Septoria tritici and 5. graminum are probably 
identical, the fungus at hand must be designated 5. tritici Desm., in one 
case on account of morphology, and in the other on account of priority. 
Yet circumstances indicate that the organism is the same as that often 
reported as injuring wheat and other cereals and called 5. graminum (4, 14, 
16, 19). It is well to note, however, that all the inoculation experiments, 
the results of which are summarized in diagram 4, were made with spores 
taken from the leaves of volunteer wheat collected in late fall or winter. 
Seedlings grown in flower pots were used exclusively for inoculation 
with Septoria tritici. Following inoculation, the bags were placed over the 
pots for three days, but were removed temporarily each day to atomize 
the leaves with water. On the fifth to the sixth day yellow spots began to 
appear on the leaves of wheat. These spots enlarged and coalesced until 
half or more than half of the blades were yellow and drooping. Unless 
the plants in the greenhouse were covered with bags for a second period or 
set in a large moist chamber, the yellow blades would dry and no pycnidia 
would develop. The first pycnidia were observed on the twelfth day, and 
were distributed in "greenish islands" of tissue, which fact showed that 
the yellowing of the entire leaf surface was not all due directly to the attack 
of the Septoria. 
That the Septoria of wheat under consideration is limited in its host 
range to the varieties of Triticum vulgar e appears conclusive from the results 
of the infection experiments given in diagram 4. In some instances, es- 
