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292 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
which influence the infection and the penetration of parasitic 
fungi. It would also be interesting to know why some fungi 
are so virulent and rapid in their destructive action on the host; 
for instance, it would be instructive to know whether it is due 
to the secretion of an enzyme, or a toxie substance (e. g., some 
acid), or to the disturbance of the osmotic relations of the host 
cells, or to some other perhaps unknown factor. For a study of 
some of these problems the writer has chosen as the organism 
Sclerotinia cinerea (Bon.) Schróter, the fungus causing the brown 
rot of stone fruits. This form is particularly suitable for the pur- 
pose since it is а virulent parasite, yet grows well as a saprophyte 
—readily lending itself to cultivation in the laboratory. 
HistoricaAL REVIEW 
Space will permit only a brief review of some of the more 
important papers dealing with certain aspects of this subject. 
Much of the literature that is indirectly concerned with the 
problem, or that is fully reviewed or superseded by subsequent 
publications, will not be discussed here. 
In the period from 1858 to 1878 little experimental evidence 
appeared concerning the nature of the action of fungous para- 
sites, although several writers make mention of the penetration 
of host cells by fungous hyphae. Penetration was then fre- 
quently spoken of as merely a process of boring through (‘‘durch- 
bohrung") the host tissue, Kühn (34), as early as 1858, men- 
"1 о: .2 this fact in a discussion of the potato-blight fungus. 
_A few years later, in 1863, de Bary (1) speaks of the penetration 
of the host by Peronospora, and further makes mention of this 
faet in connection with his work on the rusts (2); again in his 
work 'Morphologie und Physiologie der Pilze, Flechten, und 
Myxomyceten’ (3) he discusses the penetration of the host, but 
says he has no knowledge of the force that causes this boring 
into the host tissue. 
Hartig (26), in his early work on wood-destroying fungi, as 
well as in his later investigations, emphasizes the fact that fungi 
are able to destroy cellulose. Ву а microscopical study of 
diseased wood he found that the properties of the latter are 
very materially c»anged by the fungus; he did not, however, 
attempt to isolate an enzyme. 
