solve. If too immature when picked apples will wilt in storage and be poorly colored and unattractive in appearance; they will be of poor quality and lacking in aroma and flavor when they reach prime eating condition; and many varieties will be very likely to develop bad storage scald. On the other hand, it is very important that certain varieties be picked before becoming overripe. Internal breakdown-the softening and discoloration of the flesh of such varieties as Jonathan and, more rarely, Grimes Golden, Stayman Winesap, Delicious, Esopus Spitzenburg, and others appears to be associated with allowing the fruit to remain too long on the trees. The development of water-core also appears to be associated with overmaturity on the tree.

Various tests are used by growers to determine the proper time of picking apples. The color of the seeds, the ground color or color of the unblushed portion of the fruit, the extent and intensity of the blushed surface, the ease of separation of the fruit from the tree, and the apparent firmness of the flesh are used to determine the time when the fruit is in proper condition to be removed from the tree. Extended critical studies have not heretofore been made to determine the exact dependability of these various tests, particularly for fruit growing under the various climatic conditions prevailing in different parts of the country or in the same section from year to year. Consequently, a series of investigations was inaugurated by the United States Department of Agriculture in cooperation with several State agricultural experiment stations to study carefully the changes which take place in apples as they approach maturity on the tree.

The most prominent of these changes are (1) increase in size, (2) change in color of seeds, (3) change in the color of the unblushed portion of the fruit, (4) development of blush or red color on colored varieties, (5) progressive softening of the fruit, and (6) change in the tenacity with which the fruit adheres to the tree.

It was proposed to study all these changes in order to determine if possible (1) which of them constitute the most reliable criteria for judging when the fruit is ready to be picked, (2) how these ripening changes differ in the same variety when grown in different sections of the country under widely varying climatic conditions, (3) the effect of a long or short growing season on the time of ripening of the variety, and (4) whether an early bloom necessarily indicates early ripening and a late bloom late ripening.

EXPERIMENTAL METHODS

In order to obtain standard observations on the fruit, an attempt was made to eliminate so far as possible the variations in observations due to the personal factor. The general outline of the observations and tests was carried on simultaneously in the experimental orchards at Amherst, Mass.; Ithaca, N. Y.; East Lansing, Mich.; Wooster, Ohio; Council Bluffs, Iowa; Rosslyn, Va.; and in commercial orchards at Wenatchee, Wash.

Observations and tests were made at 10-day intervals, starting several weeks prior to picking dates in the different sections, as follows:

Increase in the size of the fruit.—In each orchard 100 apples of each variety were selected, tagged, numbered, and the largest radial circumference measured in centimeters at the beginning of the test. These apples were remeasured at 10-day intervals to determine the growth increment. Thus, the rate of growth and the length of time growth continues have been determined. Individual apples that dropped prior to the last measurement were eliminated from all

averages.

Hardness of the fruit.-A mechanical tester similar in essential details to that described by Murneek (15)2 for determining the hardness of the fruit was used. The number of pounds pressure required to force a smoothly rounded plunger seven-sixteenths inch in diameter into the fruit to a depth of five-sixteenths inch was determined. The tests were made with the peel intact and with the peel removed, but since the latter tests are considered the more reliable all the data presented on hardness of the fruit are based on tests directly on the flesh of the apple (with the peel removed). In most cases 30 representative apples of each variety were used for each test, and three individual tests were made about the radial circumference of each apple. These 90 tests have been averaged to represent the pressure tests, i. e., hardness of the fruit on the different dates.

Changes in the ground color or color of the unblushed portion of the fruit. In order to determine the changes in the ground color of the fruit from week to week, a chart was made up, representing as nearly as possible the color changes through which the unblushed portion of most apple varieties pass as they approach maturity on the tree. A reproduction of the chart used is shown as Plate I. The exact colors in different varieties of apples vary greatly, but by comparison with the chart the ground color of the fruit at any particular time could be fairly accurately placed. Instead of attempting to describe the color, the fruit was designated by its chart number according to the shade most nearly represented. Thus, No. 1 represents a very green shade and Nos. 2, 3, and 4 represent successive stages of yellowing; fruit falling between Nos. 2 and 3, for example, is called 22. Similar charts were used in all districts, so that the color comparisons are believed to be accurate and directly comparable.

Increase in the blushed surface of the fruit. Careful estimates of the area of the blushed surface of the 30 apples used for testing were made at each testing date. The averages presented give a fairly good indication of the change in blushed surface from time to time in the different sections.

Change in the color of the seed.-The color of the seeds was noted when the different tests were made. The time of turning brown and when full light brown are the really definite points in seed-color change and have been particularly noted.

Ease of separation from the spur and extent of dropping.-General notes were made on the ease of separation of the fruit from the spur and on the extent of natural dropping from the tree at the time of the different tests.

Numbers (italic) in parentheses refer to "Literature cited," p. 64.

SOIL AND CULTURAL CONDITIONS

The soil and cultural conditions prevailing in the different orchards in which the test trees were selected may be summarized as follows:

Rosslyn, Va.-The orchard at the Arlington Experiment Farm, located across the Potomac River from Washington, D. C., is in grass sod on loam soil. During 1923 no fertilizer was applied. In the spring of 1924, 5 pounds of nitrate of soda and 5 pounds of superphosphate were applied to each tree prior to blossoming.

Amherst, Mass.-The soil is a stony loam. In 1923 the Baldwin and Delicious trees were in sod, with nitrate fertilizer added. Ben Davis, Winesap, and Jonathan were given stripped cultivation, with 5 pounds of nitrate to each tree, while the Grimes Golden was under cultivation, receiving no nitrate. In 1924 Baldwin and Grimes Golden were in sod, with nitrate, while Ben Davis, Delicious, Winesap, and Jonathan received stripped cultivation, with nitrate. Council Bluffs, Iowa.-The trees are on silt-loam soil in clover sod, which is reseeded every three years, so the orchard is cultivated every third year. No fertilizer was applied.

Wooster, Ohio.-This soil is a silt loam. The orchard is in sod mulch and receives nitrate applications in the spring.

East Lansing, Mich.-Delicious, Jonathan, Winesap, and Baldwin received cultivation annually until 1920, when clover was sown, and since then have been in clover sod. No fertilizers have been added. Ben Davis has been in sod for many years.

Ithaca, N. Y.-The soil is a heavy loam. The trees are 12 to 14 years old and receive cultivation annually, with a weed cover crop. No fertilizers are added. The Baldwin crop was light; the other varieties had an average yield.

Wenatchee, Wash.-The soil for the Jonathan and Grimes Golden. is a fine sandy loam; the Ben Davis and Winesap trees are growing in loam soil, and Delicious trees in sandy soil. Ben Davis, Winesap, and Delicious trees received abundant water, but the irrigation of the Jonathan and Grimes Golden trees was somewhat irregular and scanty. All trees were in alfalfa sod. Ben Davis and Winesap received in addition 3 pounds nitrate of soda per tree.

WEATHER CONDITIONS

Table 1 shows detailed mean temperatures and precipitation by months at the different stations, as reported by the United States Weather Bureau. It is apparent from this summary that there was a very fair distribution of moisture through both years in those regions which depend on natural rainfall. At nearly all stations the mean temperatures for 1923 were somewhat above those for 1924 during May, June, July, and September; the mean temperatures in August, 1924, were somewhat above those for 1923. On the whole, the season of 1924 would be characterized as cool throughout all the eastern section of the United States. In the Wenatchee district of Washington the mean May temperature was about 6° F. above normal for the month; the remainder of the season averaged very close to the mean for that section.