CORRELATION BETWEEN SIZE OF THE FRUIT AND THE 
RESISTANCE OF THE TOMATO SKIN TO PUNCTURE 
AND ITS RELATION TO INFECTION WITH 
MACROSPORIUM TOMATO COOKE 
J. ROSENBAUM AND ChARLES E. SaNDO 
That artificial infection with Macrosporium tomato Cooke^ from tomato 
on uninjured tomato fruit can be obtained, provided fruit of a certain 
maturity as measured by size is used, has been established by one of the 
writers.^ The question naturally arises as to the cause of this apparent 
immunity or resistance in the fruit after it reaches a certain maturity. 
Previous investigations along these lines have been recently reviewed 
and summarized by Hawkins and Harvey^ as follows: "It is apparent that 
there is good evidence that some parasitic plants make their way into 
their host plants by breaking through the tissues mechanically. There is 
no doubt that some fungi secrete enzymes which break down the cell walls 
of certain plants and are thus able to make their way through the tissues 
of their hosts." 
The same workers from their infection studies with Pythium on potato 
conclude: "There is considerable evidence that the main factor in this 
penetration is the growth pressure of the fungus filament, and the resistance 
of the white McCormick potatoes to this disease is due to cell walls that are 
more resistant to mechanical puncture than are the cell walls of extremely 
susceptible varieties." 
The results obtained by Blackman and Welsford^ in their studies with 
Botrytis cinerea on Vicia Faha are of special interest. They state that 
"the piercing of the cuticle is due solely to the mechanical pressure exerted 
by the germ tube as a whole or by the special outgrowth from it." 
In the work reported in this paper the evidence obtained shows that: 
I . While a chemical difference is found in the analysis of young and old 
fruits, this is not the limiting factor in infection with Macrosporium. The 
1 The fungus causing typical "nail-head" spots on tomatoes has been shown in a 
paper which is being prepared for pubhcation to be different from Macrosporium solani 
E. and M. For reasons given there this Macrosporium should be referred to as Macro- 
sporium tomato Cooke. 
2 Rosenbaum, J. Macrosporium solani on tomato fruit (Abstr.). Phytopathology 
9: 51. 1919. 
3 Hawkins, L. A. and Harvey, R. B. Physiological study of the parasitism of Pythium 
deharyanum Hesse on the potato tuber, Journ. Agr. Res. 18: 275-297. 1919. 
4 Blackman, V. H., and Welsford, E. J. Studies in the physiology of parasitism. 
H. Infection by Botrytis cinerea. Annals of Botany 30: 389-398. 1916. 
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