598 
Journal of Agricultural Research 
Vol. XXXI, No. 7 
whether one or more species were involved; (2) to make cross inocula¬ 
tions with these cultures, to see whether or not there were any 
specificities which cause certain strains to infect definite hosts; (3) to 
make temperature studies of these fungi; (4) to determine the r6le of 
the microconidia in the life history of the genus Sclerotinia. 
The material and cultures used in the following studies were all 
collected by the writer, on the Chicago market, with the exception of 
a few strains, for which due credit is given in the footnotes. Material 
from practically every State has been collected and cultured. This 
has offered an admirable opportunity to compare strains of the genus 
Sclerotinia from all of the important truck-crop regions, and it is 
believed that the studies given here will be of special value in that 
such a wide geographical range and large variety of hosts were con¬ 
sidered. The literature of the subject abounds with such excellent 
descriptions of the field diseases caused by Sclerotinia that it is felt 
hardly worth while to do more here than cite some of the more import¬ 
ant articles. While the bibliography at the close of this article does 
not pretend to be complete, it is hoped it will furnish a working basis 
for any who may be interested in this subject. 
ECONOMIC IMPORTANCE 
Among the numerous fungi that are important in causing diseases 
in vegetables under transit, storage, and market conditions, members 
of the genus Sclerotinia rank well toward the head of the list. This 
fact has been especially noticeable since the establishment of the 
Food Products Inspection Service by the Bureau of Agricultural 
Economics of the United States Department of Agriculture. More 
than 30,000 inspections of perishable fruit and vegetable produce are 
now made at the receiving markets annually, and the inspectors’ 
certificates on car-lot shipments covering a great number of vegetables 
show a surprisingly large loss due to decay caused by Sclerotinia 
species. In their studies of the market diseases of vegetables, Link 
and Gardner {20) adopted the term “watery soft rot” to describe 
the decay caused by S . libertiana, and said: “In the market it occurs 
on a wide variety of hosts. It is the prevalent rot at low tempera¬ 
tures, and is the most important storage rot of root crops.” The 
type of decay produced varies somewhat with the different species 
and the different hosts, but there are some outstanding character¬ 
istics which are usually common to all. Chief among these is the 
soft, watery, odorless type of decay. If the host tissue is free from 
other contaminating organisms, it may become so completely pene¬ 
trated by Sclerotinia mycelium that practically all of the water will 
be liberated without odor. In fact, the liberated juice of the host 
seems to increase the natural odor of the plant. A second char¬ 
acteristic is the abundant white cottony mycelium which is present 
on the surface of the host in a humid atmosphere, and the black 
sclerotia which are formed in the old mycelium in regions where the 
host tissues are partially consumed (pi. 1, B, C, H). The sclerotia 
are normally produced on the surface of the host, but in some in¬ 
stances under field conditions they are formed within the pith of 
stems, such as those of the potato, tomato, sunflower, and the seed 
stalks of lettuce (pi. 1, A). In such cases the sclerotia are often 
