19i2] REY NOLDS—PARASITIZED LEAF TISSUE 389 
poisonous substance which directly affects the host cells, as WARD 
(86) claims for the Botrytis fungus that causes the lily disease. 
WoroNIN (930) attributes in an inferential way the effect of 
Sclerotina Vaccinit upon the cowberry to the same process. TUBEUF 
(80) quotes from him thus: ‘‘Here a peculiar phenomenon is exhib- 
ited, the fungus exerts its injurious effects on the surrounding 
tissues of the host plant, then, having killed these, it utilizes them 
as food material.”” Thus the tissues are killed first, apparently 
even beyond the immediate vicinity of the fungus, and are later 
used for food. That the parasitic fungi upon leaves produce this 
toxic substance is more easily believed than that the host produces 
it, and is itself killed by the protective measure. The nature of 
the poisonous substance, whether a chemical organic poison or an 
enzyme, could not be determined in the material at hand. 
Another interesting question, whose answer may be at least 
partly suggested, has to do with the strict limitation of certain 
leaf-inhabiting fungi, such as the shot-hole fungi. This strict 
limiting of the area of influence of the fungus is shown in the 
Smilax disease described earlier in the paper. At the margin of 
the diseased area the leaf cells are killed and turned a deep brown 
to black. This discoloration may be due to the excessive produc- 
tion of tannins, and if so, this would probably explain why the 
fungus proceeds no farther. Boxkorny (50) has found that tannins 
will inhibit the growth of fungi, and it seems quite likely that the’ 
production of tannins in the leaf finally stops the further growth 
of the fungus. 
| Summary 
In the review of the previous work, it was found that many 
changes have been noticed in the organs and tissues of flowering 
plants. The cytologic changes, however, were especially empha- 
sized. Very little work has previously been reported upon the 
effect of fungi on the cell contents of leaves, and the writer has 
shown that in such cells the nuclear and protoplasmic changes, 
which other workers have noted in cells of other plant organs 
attacked by parasites or under the influence of other destructive 
agents, also occur in leaf tissues when attacked by the parasitic 
fungi examined. 
