28 MISC. PUBLICATION 49 8, U. S. DEPT. OF AGRICULTURE 



occurs. After a few days, however, additional symptoms appear. 

 First and most characteristic among these is a buckling of the parti- 

 tion walls at the stem end of the fruit, with or without drying of the 

 pulp (pi. 16, A and B). Small pits or pitted areas may also develop 

 in the rind on any part of the fruit. In fruit on the market, picked 

 several days after it had been frozen on the tree, the injury is mani- 

 fest by woodiness of the pulp or by open spaces between the segments 

 due to the collapse and drying out of some of the juice sacs. Cavities 

 usually appear in the orange pulp before open spaces develop between 

 the segment walls. Later, when considerable drying out of the pulp 

 has occurred, small open spaces between the segment walls may be 

 found. Sometimes only one or two segments will show drying-out 

 effects and all or only a part of the segment may be affected/ Where 

 only one or two segments are affected, considerable time is required 

 for them to dry an inch or more. 



There are, of course, all degrees of dryness, from very slight to total. 

 In the practical handling of citrus fruit three degrees are recognized: 

 (1) Slightly open, when the cut surface shows a slight open space be- 

 tween the segment walls and the juice sacs but the surface of the pulp 

 appears juicy. (2) Distinctly open, when the cut surface shows large 

 open spaces but the pulp still appears juicy. (3) Dry, when the cut 

 surface shows no large open spaces but the fruit seems to have dried 

 out evenly all through and the color of the pulp shows it to be almost 

 devoid of juice, or when the fruit has dried out with some of the seg- 

 ments more or less collapsed. 



Drying in oranges usually progresses from the stem end, whereas 

 in grapefruit it may proceed from either or both ends or it may begin 

 around the outside of the pulp. Drying is not found at the center of 

 the fruit except in extreme cases. If an orange that has been frozen 

 is examined a few days after it thaws, it will usually show the hesperi- 

 din crystals already mentioned on the membrane or rag that separates 

 the segments of the pulp. On the other hand, the crystals are some- 

 times visible when examination is made within a few hours after the 

 freezing, whereas if it is not made until several weeks afterward they 

 may not be so numerous or conspicuous, probably because the more 

 severely frozen fruit falls soon after the freeze. In frozen tangerines 

 the crystals may occur in the pulp as well as on the membrane between 

 the segments. When examined on the market, tree-frozen fruit that 

 has remained on the tree for several weeks after freezing has a rind 

 that is thicker than normal, especially over the damaged part of the 

 fruit. 



As differentiated from granulation, dryness from freezing results 

 through the empt3 T ing and subsequent collapse of juice sacs due to dis- 

 appearance of the juice. In granulation the juice sacs do not collapse 

 but become filled with gelatinous or solid matter. 



(See 3, 43, 60, 96, 133.) 



FUMIGATION INJURY 



Fumigation with hydrocyanic acid gas may cause injury to the 

 fruit, leaves, young twigs, and trunks of citrus trees. The common- 

 est form of the injury on the fruit occurs as pits of various sizes 

 ranging from mere pin points to sharply sunken areas a quarter of 

 an inch across or even somewhat larger. At first these have about 



