Mar 8, 1924 
Nocturnal Production of Sclerospora 
775 
conidiophore production as a result of local differences in amount or 
time of dew deposition. 
How long Sclerospora graminicola may continue noctumally producing 
conidia on infected Setaria plants, how tolerant of this continued pro¬ 
duction the host may be, and how much of its life span may be taken up 
* by the conidium-forming period of the fungus, are points which, in this 
case, were not worked out in detail as they had been for the Philippine 
Sclerosporas (32). In one case, however, even* though the transplanted 
Setarias grew very poorly, one plant showed intermittent conidiophore 
formation for more than two weeks. Also, in the field, there is abundant 
evidence that the period of conidium production continues much longer 
than this, even extending over as great a proportion of the total life of 
the host as did the Sclerosporas studied by the writer (32) on maize 
in the Philippines. 
A study of large numbers of S.-gramm^cc/a-infected Setaria plants 
of various ages in the fields near the College of Agriculture at St. Paul, 
Minn., showed the progress of the disease to be as follows: Production of 
conidia begins on newly unfolding leaves in symptomatically chlorotic 
streaks which, by their extent and position even in very young plants, 
indicate a fundamental systemic infection starting in the young seedling 
and giving rise to thorough and extensive invasion of the host tissue. 
The production of conidia continues during each favorable night on these 
earlier leaves, and also continually starts up afresh on leaves successively 
appearing. Gradually, as the host matures, conidiophore formation from 
the host surface is superseded by the development of oogonia on the 
intramatrical mycelium, beginning in the lower, first unfolded, older 
leaves, and working slowly upward. The uppermost, latest, and youngest 
leaves are the last to be affected, and may continue abundant conidi¬ 
ophore production until the head, usually deformed, sterile, and vires- 
cent, is full grown. Finally, however, even these ultimate leaves also 
are given over to oogonium formation, and show the shredding of tissue 
which marks the maturity of the oogonial phase of the fungus. 
The conidial stage of Sclerospora graminicola , because its relation to 
nocturnal moisture has not been understood, has been considered from 
the time of Schroeter to the present as fleeting, transitory, fugacious, and 
evanescent. Now, however, that we know the period of conidium pro¬ 
duction may be of relatively long duration, we must alter our conception 
of the evanescence of the conidial stage. It is fugacious in the sense 
that conidiophore production takes place for only a few hours during 
the night; but it is decidedly persistent in the sense that this production 
may go on night after night throughout a-large proportion of the total 
life of the host. 
CONIDIAL SCLEROSPORA GRAMINICOLA COMPARED TOOTHER SPECIES 
Material of the conidiophores and conidia of Sclerospora graminicola 
gathered thus at night during the period of optimum conidiophore 
production is infinitely more satisfactory for study than the dried and 
shriveled remnants which persist from previous nights and may be 
collected during the day.- Consequently, such material gives a somewhat 
broader conception of the character of the species than that which we 
gain from the usual descriptions and figures based on dried material, 
and also permits a more adequate comparison with the conidiophores 
and conidia of other species. 
