1919] HORTICULTURE. 539 



soda gave much better results as a carrier of nitrogen than lime nitrogen. In 

 one set of experiments the best results were secured by alternating a dressing 

 of organic manure one year with a dressing of a complete commercial fertil- 

 izer the following year. Better results were secured when a complete fertil- 

 izer was used than when one of the elements was omitted. 



A study of the effects of freezes on citrus in California, H. J. Webbek et al. 

 (California Sta. Bui. 304 (1919), pp. 243-321, figs. 23).— A bulletin of informa- 

 tion for citrus growers summarizing the results of general field studies and 

 observations, as well as special studies conducted following the great freeze 

 of January 5-7, 1913. The subject matter is presented in three papers, as 

 follows : 



A study of the freeze of 1913 in California, by C. S. Milliken, A. R. Tylor, 

 W. W. Bonns, and H. J. Webber (pp. 249-298 ) .—This paper is essentially a 

 record of the freeze of 1913, based on a survey made in a number of different 

 districts by many different observers. Information is given relative to the 

 effects of the freeze upon citrus trees, foliage, wood and bark, on the external 

 appearance of fruit, on the internal condition, and on the quality and uses of 

 the fruit ; method of determining the extent of fruit injury ; relative hardiness 

 of trees and fruit of different species and varieties of citrus; natural factors 

 influencing the temperature, such as elevation, protective hills, canyons, bodies 

 of water, and location of fruit on the tree ; artificial methods of protecting 

 groves, such as windbreaks, irrigation, spraying, wrapping the trees, lath 

 houses, burlap or cloth coverings ; and protection by artificial heating. Con- 

 siderations are also given factors influencing resistance of trees to cold injury, 

 treatment of frozen trees, and aftereffects of the freeze on the trees and fruit. 

 Methods employed in separating good fruit from frozen fruit are described. 



Changes that take place in frozen oranges and lemons, by E. E. Thomas, 

 H. D. Young, and C. O. Smith (pp. 299-314). — The work here reported was car- 

 ried out at the citrus substation following the freeze of 1913, with the view of 

 determining the nature and rate of change that takes place in frozen fruit. 

 Special consideration was given to a comparison of the specific gravity, average 

 weight, and percentage and total amount of sugar and acid in frozen and sound 

 fruit. See also previous notes (E. S. R., 34, p. 365; 36, p. 416). The results 

 are here presented in tabular form and discussed. 



Generally speaking, the specific gravity of frozen citrus fruits was found to 

 be lower than that of unfrozen fruits. Although there is a certain overlapping 

 of the two classes, the division is sufficiently complete to make it commer- 

 cially practical to separate frozen fruit by the specific gravity test. In lemons 

 the changes in specific gravity are more rapid than in oranges. The specific 

 gravity of sound fruit increases under storage and the specific gravity of frozen 

 fruit decreases. A month is generally long enough to make a recognizable 

 difference, but better separations can be obtained after six weeks or two 

 months. 



The excessive loss of moisture in citrus fruits caused by freezing is due to a 

 change in the walls of the cells from semipermeable membranes to a porous 

 substance that freely allows the liquid to evaporate from the interior without 

 decreasing its volume. Frosted citrus fruits that remain on the tree continue 

 to increase in size, this development being a thickening of the rind. 



The total amount of sugars decreases in frozen fruit, although no change was 



found in the relative amounts of the different sugars present. The percentage 



of acid in the juice of frozen citrus fruits decreases slightly as compared with 



the unfrozen. The weight of acid per fruit in unfrozen fruit remains nearly 



114878°— No. 6—19 4 



