. Bulletin. Natural history; Natural history. Diseases of Frtjit Trees, 1922-1928 499 this respect, the plum third, the cherry fourth, and the pear, with its one important disease, fifth. But it is interesting to find that in suscepti- bility to disease attack the apple also ranks first, and this is true in spite of the larger number of apple diseases. On an average, an apple dis- ease succeeds in attacking 68 or 69 out of every 100 trees. Avhile a peach disease succeeds in attacking only 55 trees in a hundred. The average susceptibility of the plum and cherry to disease attack appears rather
. Bulletin. Natural history; Natural history. Diseases of Frtjit Trees, 1922-1928 499 this respect, the plum third, the cherry fourth, and the pear, with its one important disease, fifth. But it is interesting to find that in suscepti- bility to disease attack the apple also ranks first, and this is true in spite of the larger number of apple diseases. On an average, an apple dis- ease succeeds in attacking 68 or 69 out of every 100 trees. Avhile a peach disease succeeds in attacking only 55 trees in a hundred. The average susceptibility of the plum and cherry to disease attack appears rather high when the figures given in Table XXIV are interpreted strictly, being respectively 67 and 77 trees per 100; but since the leaf spot disease, as recognized in the accumulation of data, is in each case really a composite of two diseases, their apparent susceptibility is re- duced thereby to about 44 and 48 trees per 100, respectively, or less than the susceptibility of the peach. From the graphical presentation of data in Figure 31, it may be seen that the differences between kinds of fruit-trees that have been shown to exist with relation to disease pre- valence are neither constant nor parallel with relation to the intensitv of APPLE PEAR FEACh CMERRy PLUM ^^â â 22/ â â /.34 0 I 2 3 4-0 10 ZO iO 40 50 0 10 ZO do Incidence rruit Intensltu Twio Intenoitu 0 5 /a 15 Leaf Intenaltu Fig. 31. Comparison of the average ainnual prevalence and intensity of DISEASE on fruit TREES IN ILLINOIS The data given in Table XXIV are presented graphically for ready comparison. Incidence of disease shows the average number of diseases attacking each kind of fruit tree, and the total intensity of the attack of these diseases is shown for fruit, leaf, and twig. See text for discussion. Table XXIV Average Annual Prevalence and Intensity of Fruit-tree Diseases in Illinois, as Determined From Data Covering the Period 1922-1928 Kind of tree Xumber of diseases included Incidence o
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