50 DIPLODIA CORCHORI SYD. 
(d) On 18th September at 4-30 p.m. 11 plants were infected. Six plants were 
killed by the fungus. 
In this experiment, therefore, there were marked differences in the results 
with a series of identical infections. The controls remained healthy 
throughout. 
Experiment XVII. On 14th September at 11 a.m. twelve plants of red~ 
stemmed C. olitorius were infected. The infections were carried out upon the 
uninjured stem and were covered with small strips of cloth as in the previous 
experiment. Ten infections took, producing the typical “ black band” on the 
stem. The experiment was closed before the plants were killed by the fungus. 
Experiment XVIII. All infections in this experiment were carried out on 
late sown plants of green capsularis ; the plants were grown in pot cultures from 
seed sown on 20th June. 
(a) Three plants, each about 12” high, were infected on 23rd July at 10 a.m. 
All infections were jacketed with lamp chimneys, and three controls, consisting of 
plants with a minute piece of sterile agar on the stem, were also jacketed. On 
27th July one of the infected plants was dead, the remaining plants, both inoculated 
and controls, remained healthy. 
(b) This experiment was a repetition of the last ; the infections were made on | 
7h August at 11 a.m. Of three plants infected one was killed by 4th August 
—the remaining infections did not take. 
(c) On 25th July at 10 a.m. twelve plants were infected ; these plants were 
not jacketed with lamp chimneys and the pots were standing in the open air on a 
verandah. One plant was killed by the fungus, the remaining 11 plants were not 
affected, the moculum drying up. 
(2) On 10th August at 10 a.m. these eleven plants were again infected. Six 
of the infected plants were killed by the 14th August and three more died by 23rd 
August (Pl. VI, fig. 2). 
Factors in the Incidence of the Disease. 
Evidence has clearly shown that D. Corchori has been widely diffused in Bihar, 
Bengal and Assam for many years past ; therefore in the season 1917, when the 
disease was bad, there must have been some factors favourable to the appearance 
of “ black band,” which were not acting in 1918 or 1919, when the incidence of the 
disease was much less severe. 
The analysis of the factors which produce any epidemic is a task of great 
difficulty, since of the numerous causes to be evaluated each has to be considered 
in relation to both parasite and host. Thus a disease may increase in virulence 
owing to some change in the host which renders it a more favourable medium for 
