256 
Journal of Agricultural Research 
Vol. VII, No. s 
weight of a carbohydrate that would produce the necessary osmotic 
pressure. The present writer (7) germinated the conidia of Glomerella 
cingulata and grew the fungus in concentrations of calcium nitrate, potas¬ 
sium nitrate, and sucrose, which had diffusion tensions of 29.1, 39.3, 
and 47.3 atmospheres, respectively. 
Dorn (3), in his study on the penetration of plant membranes by fun¬ 
gus hyphae, mentions that there is an osmotic pressure of about 50 atmos¬ 
pheres in fungus hyphae. 
It seems probable from a consideration of the question and from the 
work that has been done that fungus parasites should be able to live 
and grow in solutions of a considerably higher concentration than the 
total concentration of the cell sap of their host plants. It was considered 
worth while, however, to obtain more evidence on this point. Ten com¬ 
mon parasitic fungi were grown in solutions of salts and sugars of rather 
high concentrations. The total diffusion tensions of the dissolved mate¬ 
rials in the expressed juice of some of their host plants was determined 
by the freezing-point method. The present paper deals with this work. 
The fungi 1 studied were Fusarium radicicola Wollenw. and F. oxy - 
sporum Schlecht., two potato-rotting fungi (2); Plenodomus destruens 
Harter, Diplodia tubericola (E. and E.) Taub., Sphaeronema fimbriatum 
(E. and H.) Sacc., and Rhizopus nigricans Ehrenb., which are parasitic 
upon sweet potato (6), and Botrytis cinerea Pers., Sclerotinia cinerea 
(Bon.) Schroter, and Sphaeropsis malorum Peck, well-known parasites 
on the apple fruit. A strain of Rhizopus nigricans Ehrenb., which causes 
a serious rot of the strawberry (16), was also used. The data on the dif¬ 
fusion tension of the solutions in which Glomerella cingulata (Stonem.) 
S. and v. S. was grown are taken from an earlier paper by the present 
writer. Several of these fungi are parasitic on more than one of the hosts 
mentioned. The lowering of the freezing point of the expressed juice 
of apples (Malus sylvestris ), sweet potatoes ( Ipomoea batatas) , potatoes 
(Solanum tuberosum ), and strawberries (Fragaria spp.) was determined. 
In the experiments with the fungi two methods were followed for the 
determination of the highest concentrations of the various substances 
used in which the fungi could grow. In the one method hanging-drop 
cultures were made of the spores which had been sown in salt or sugar 
solution of varying concentrations. These cultures were examined by 
means of a miscroscope, and the highest concentration in which the 
germination was apparent was noted. The other method was similar in 
principle to the one just outlined. In this the procedure was to sow the 
spores in sterilized tubes of the salt (sodium chlorid) or sugar solution and 
after about a week determine the growth or lack of growth by observation. 
1 The writer’s thanks are due Mr. C. W. Carpenter for cultures of the species of Fusarium, Mr. L. L. 
Harter for cultures of the fungi from sweet potato, Dr. J. S. Cooley for the apple-rot fungi, and Dr. Neil E. 
Stevens for cultures of the species of Rhizopus from strawberry. 
