Mar. 3 ,19 23 
Gray Mold of Castor Bean 
687 
diseased field disclosed the first appearance of sclerotia under natural 
conditions. These were found upon the diseased spikes usually at their 
bases upon wood that still contained some sap. Plate 1 and Plate 5 A, 
show some typical examples of this condition. From this time on 
sclerotia could be found in increasingly greater abundance. 
Before the middle of the month there were found sclerotia lower down 
on the stalk of the plant. It was soon obvious that spurs that had become 
infected during the first growing season were instrumental in carrying 
the infection into the cambium layer of the stalk. Here the fungus 
overwintered. With the advent of growing conditions, coupled with the 
decreased resistance of the host plant, it started again into active growth, 
which was semisaprophytic, in all probability, rather than purely para¬ 
sitic. Sometimes a distinct canker could be seen, with a molded spur 
in the middle (PI. 5, B, C). Sclerotia soon became evident, growing 
up through the cortex, sometimes evident on the surface only as a hump 
(PI. 6, C), and again practically formed on the surface. Plate 6, A 
and B, are standing plants with an abundance of surface sclerotia. For 
the next two or three months stalk-borne sclerotia were to be found 
more and more. Many newly formed cankers with subsequent sclerotia 
were traceable directly to spring infections of new spurs that had started 
from buds on the staiks. 
In early summer the coffee-bean weevil, Araecerus fasciculate De G., 
listed among the corn-destroying weevils of the South by Cotton (5), 
was frequently seen on castor-bean plants of the previous season’s 
growth, and the interesting observation was made that it was actually 
eating the sclerotia of Sclerotinia ricini Godf. Several of the weevils 
were caught and imprisoned and furnished with sclerotia and com as 
food. They appeared actually to prefer the sclerotia to the com. No 
significance is attached to their liking for this fungus as food, however, 
since they scarcely made an impression on the sclerotia that were 
available. 
CAUSAL ORGANISM 
ISOLATION 
The organism was very easy to isolate. Any portion of a diseased 
inflorescence placed upon a poured plate of potato or com meal agar at 
ordinary temperatures would develop the fungus rapidly, and as a rule 
it would outgrow all contaminating fungi or bacteria, and pure culture 
transfers could be readily made. In order to obtain definite strains of 
the fungus, however, the writer followed the precaution of obtaining 
single spore cultures in practically every case. This was done by lifting 
in a pair of forceps a small tuft of the fruiting fungus from the diseased 
material, holding it at the edge of the poured plate and giving a quick 
blow with the breath, thus blowing spores upon the surface of the plate. 
The method was suggested by Prof. H. H. Whetzel, who uses it largely 
in his work with Botrytis. Clear corn-meal agar was used by the writer. 
Inside of 24 hours well-isolated single spores, already germinating, were 
picked out and transferred to tubes. In case any particular plate was 
too thickly sown with spores, or an absolutely sure single spore isolation 
was in any other way doubtful, transfers were made to another plate of 
clear agar and the growth of the colony was followed to make sure of its 
purity. 
In this way about 50 original isolations of the fungus were made. 
The sources and dates and particular information concerning them are 
listed in Table I. 
