oct. i, 1925 Sclerotinia Species Causing Decay of Vegetables 
605 
gave sclerotia which would average less than 1 mm. in diameter. 
After several transfers on potato-dextrose agar, the sclerotia were 
2 to 5 mm. in diameter, with an average diameter of about 3 mm. 
This leads one to suspect that the fungus had become better adapted 
to the artificial medium. Gilbert and Bennett (If) found in their 
study of Sclerotinia trifoliorum Erik, that large sclerotia were pro¬ 
duced on favorable media such as potato plugs, while on unfavorable 
media the sclerotia were small. This undoubtedly explains why the 
sclerotia on the host plant are often quite different from those of the 
same fungus when grown on artificial media. From these observa¬ 
tions it is quite evident that while the size of the sclerotia may be 
useful in separating species, this character can not be depended upon 
unless the influence of temperature and culture media are taken into 
consideration. 
The sclerotia of S . minor and S. intermedia have showed constant 
differences from those of S . libertiana throughout all experiments. 
In all cultures of the large sclerotial type there were no appreciable 
differences in the sclerotia of the strains studied that could not be 
attributed to growing conditions. As it is fair to compare only 
sclerotia that have been grown under exactly parallel conditions, 
the following data will suffice to show the relative size of sclerotia 
of the strains of Sclerotinia under consideration. * On plate cultures 
of oat-nieal agar, the large sclerotial strains produced sclerotia 
ranging from 2.5 to 6 mm. in diameter, averaging 3.5 mm. In similar 
cultures of S . minor the range was 0.5 to 1 mm., average 0.78 mm. in 
diameter, while the sclerotia of S . intermedia ranged from 1 to 3 mm. 
in diameter, with an average of 2 mm. These species cultured on 
tubes of potato agar are shown in Plate 2, E, F, and G. 
APOTHECIAL PRODUCTION 
Laboratory experiments show that no definite period of dormancy 
is necessary to prepare sclerotia for production of apothecia. Scle¬ 
rotia held in a dry state for several months do not germinate any 
more readily than “those of the same kind which are one or two 
months old. No advantages have ever been observed from chilling 
or alternating the temperatures at which the sclerotia were held. 
There are, however, differences which are traceable to seasonal or 
ecological conditions, such as the influence of light, temperature, 
and moisture. 
The development of apothecia may be divided into two phases. 
The first embraces the germination of the sclerotium and sending 
forth of the hornlike stalks; the second involves the development of 
the funnel-shaped top and its ultimate expansion into the disklike cap. 
Experiments show that germination oi the sclerotia is dependent 
upon proper moisture and temperature conditions, while the main 
factor for the development and full expansion of the apothecium is 
light. 
Best results in the laboratory have been obtained by planting 
mature sclerotia 5 to 10 mm. deep in sterile sand in an ordinary porous 
flower pot (pi. 2, A and C). Four-inch pots placed in saucers or 
halves of Petri dishes filled with sterile water have been found satis¬ 
factory if they are placed under bell jars. The use of sterile pots, 
sand, and water has been necessary in most instances in order to 
71486—26t-2 
