A quantitative study of the course of fungal invasion of the apple fruit, and its bearing on the nature of disease resistance.—Part II. The application of the statistical method to certain specific problems

In the previous paper (1) a method was developed for studying quantitatively the process of invasion of apples by fungi inoculated into them. It was there shown that the method is capable of yielding a measure of the amount of invasion (radial advance) which is independent of the size of the apple used and of the time of duration of the experiment. The distribution of radial advance in populations of apples was studied and it was shown (1) that the distribution of radial advance (in terms of which resistance to invasion is measured) is not highly asymmetrical if measured at the right stage of invasion, (2) that an individual apple is more uniform with respect to resistance than are any two apples selected at random. It is shown in the course of the present paper that by utilising radial advance as a measure of invasion the change in resistance to the attack of fungal species during the period of storage can be followed. A comparison is made of the virulence of certain fungal species or strains and of the variation in resistance to fungal invasion shown by different populations of given varieties of apples during storage. The significance of these comparisons has been estimated by the calculation of probable errors, which was shown to be legitimate in the previous paper. Finally the bearing of the results obtained on the problem of disease resistance is discussed.