22 BULLETIN 1406, U. S. DEPARTMENT OF AGRICULTURE 



as when the fruit is ripening under cooler conditions. In the tests 

 so far carried on. the ground color of the fruits has been less yellow in 

 apples from the southern and northwestern districts than in fruit 

 from the northern and eastern sections. Different varieties will also 

 differ markedly in their tendency to take on a yellow ground color. 

 It is also undoubtedly true, although not apparent from these inves- 

 tigations, that cultural conditions, and particularly nitrogen supply, 

 are important factors in the ground-color change. Excessive nitro- 

 gen is very likely to retard the yellowing of the fruit even though 

 softening and other maturity factors are well advanced. 



The pressure test, or the test of the actual condition of firmness 

 of the flesh, is apparently a very valuable index of condition, partic- 

 ularly for certain varieties and under certain growing conditions. 

 Varieties having a growing season of medium or short length when 

 grown in districts having a long growing season may become so 

 mature on the trees that they will develop internal breakdown or 

 flesh collapse while in storage. Daly (7) has shown this breakdown 

 in Jonathan to be associated with allowing the fruit to remain on 

 the tree too long. This breakdown while particularly severe in 

 Jonathan may also occur to a certain extent in Grimes Golden, 

 Delicious, Stayman Winesap, etc., grown in the southern or north- 

 western districts, but apparently is not likely to occur unless the 

 fruit becomes too soft prior to harvest. The pressure test gives a 

 means of determining the exact flesh condition while the fruit is 

 still on the tree. 



The limit of softness to which different varieties may be allowed to 

 go before danger of internal breakdown in storage is pronounced 

 has not been studied sufficiently in connection with the extent of 

 breakdown in storage to make accurate recommendations. From the 

 results obtained, however, it may be suggested that when such a 

 variety as Jonathan shows a flesh test of 15 pounds or less it is get- 

 ting close to the danger point. A pressure test of about 18 pounds 

 on an average sample represents approximately the maximum soften- 

 ing on the tree which should be allowed in Grimes Golden, whereas 

 Delicious should not go under 16 pounds if good storage fruit is 

 desired. 



In the districts having shorter growing seasons and for varieties 

 requiring a long growing season in the early-blooming districts it 

 would appear that the fruit is usually sufficiently firm at picking 

 time. Color and the way the fruit adheres to the tree are sufficiently 

 dependable characters for determining the best time to remove the 

 apples from the tree. For the varieties heretofore mentioned, how- 

 ever, it is believed that the pressure test to determine the actual flesh 

 condition will be of great aid in preventing overmaturity and the 

 resultant breakdown in storage which so often occurs. 



In conclusion it should be emphasized that the ripening process in 

 apples is a combination of many factors, some of which appear to be 

 controlled by conditions within the tree, while others are greatly in- 

 fluenced by external conditions. The different changes taking place 

 in the fruit as it approaches maturity on the tree may continue at 

 varying rates in different seasons and under varying climatic and 

 nutritional conditions. The seeds may become brown relatively early 

 or relatively late. In one case the ground color may become yellow 



