Apple rust . d(1914, p. 15) gives some records of it. There were two rustinfections in 1911. We do not know the exact dates whenthey occurred, but one was probably just as the first blossomswere about to open and the other not until the latter part ofMay. The terminal growth on York Imperial twigs duringthat season commonly showed nine large leaves. The firstthree and last three leaves on such a growth were rust in-fected, while between them were three leaves free from was very noticeable, and was commented upon by manyorchard men. The fourth, fifth and sixth leaves must havebeen imm
Apple rust . d(1914, p. 15) gives some records of it. There were two rustinfections in 1911. We do not know the exact dates whenthey occurred, but one was probably just as the first blossomswere about to open and the other not until the latter part ofMay. The terminal growth on York Imperial twigs duringthat season commonly showed nine large leaves. The firstthree and last three leaves on such a growth were rust in-fected, while between them were three leaves free from was very noticeable, and was commented upon by manyorchard men. The fourth, fifth and sixth leaves must havebeen immune at the time that the three youngest leaves wereinfected. The same thing is clearly shown in Table XII. At thetime when the important infection took place in 1913, the firstthree to five large leaves had become immune. Table XVindicates this in relation to the Tune 4th and 5th infectionof 1914. Stewart (1910, p. 317) says, The spring of 1903 was verydry at Riverhead, Long Island. There was no precipitation. 30 W. Va. Agrl. Experiment Station [Bul. 154] of any importance between April 16th and June 8th. As aconsequence, there was no opportunity for the infection ofapple leaves until June 8th and 9th on which dates there wereheavy showers and the cedar apples became swollen into yel-low gelatinous masses of unusually large size. Very little rustoccurred on the leaves that year. Evidently most of theleaves had become immune when that infection occurred. During 1914, records were kept on several twigs showingthe exact date when each leaf finally opened out from thebud. From the data for this season it would appear that aleaf was immune ten days after unfolding. The exact timerequired for a leaf to develop to the same extent duringanother season or under other conditions, might vary some-what from this period. The points to be emphasized are that the leaves do be-come immune, (due evidently to a thickening and hardeningof the epidermal cells, as well as to other chemical and phys
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