304 University of California Puhlications in Agricultural Sciences [Vol. 3 



there is a marked similaritj' between the modes of infection. Accord- 

 ing to Longj-ear (p. 7) : 



The reason why certain varieties of the apple are particularly subject to 

 the blackened seed cavity is found in a structural peculiarity of such varieties. 

 Thus a longitudinal section through such an apple usually shows a very deep 

 calj'x tube, which, in many cases, extends to or meets the core, or even opens 

 into it. In such cases the fungus has evidently reached the core through this 

 passageway by following the united styles and the inner wall of the calyx tube. 

 (Italics ours.) 



Only certain varieties of apples, such as the Winesap, Ben Davis and 

 a few others which have the structural peculiarities above mentioned, 

 are found to be affected and in this connection Longyear's remarks on 

 page 12 are of particular interest to us. 



Some of these varieties are among those which are reported as dropping 

 their fruit badly in some seasons during June and July, but whether or not the 

 fungus plays any part in this matter has not been determined. 



The experimental work with Alternaria in 1917 for several reasons 

 gave quite different results from those obtained during the previous 

 season. As is shown in tables 3 and 4, cultures made from stigmas 

 early in the season showed a high per cent of Alternaria infection. 

 However, a very large series of cultures made somewhat later in the 

 season, from the young fruits one-half to two centimeters in diameter, 

 to our astonishment showed a very small per cent of infection. Culture 

 after culture showed no Alternaria at all. Somewhat later, when the 

 fruits were larger, cultures of the shed fruits showed a higher per cent 

 of infection, while a few cultures made when the dropped fruits were 

 four to five centimeters in diameter showed a high per cent of Alter- 

 naria infection. 



Inasnutch as by far the greater part of the drop occurs wliile the 

 fruits are one-half to two centimeters in diameter, at which time our 

 cultures showed comparatively little Alternaria infection, it is evident 

 that the shedding of this part of the crop can not be attributed to 

 Alternaria. However, it is to be noted that, as was the case in 1916, 

 toward the end of the period of shedding the dropped fruits .showed 

 a steady increase in tlie per cent -of infection. Evidently, then, the 

 shedding may be divided into two parts, the first including small fruits 

 which >nai/ or may not be infected with Alternaria, the second includ- 

 ing larger fruits which are infected with Alternaria. 



Inasmuch as the climatic conditions in the San Joaquin Valley 

 during the 1917 season were considerably more severe than in 1916 



