1919] HOrenOULTUML 839 



11, pp. 258-251; 12, pp. 277-279; 13, pp. 302-307).- In continuation of previous 



data (E. s. R., 39, p. 242), observations an- given tot the nineteenth year rela- 

 tive to the behavior of a large number of hybrid direct bearing grapes, with 



reference to their resistance to disease, adaptation to various soil condition, 

 production, etc. 



Developing new grape industries, G. C. Hussiann {PtOC. Amer. Boo, Eori, 

 Set., 15 (1918), pp. 73-79). — A summarized account of the more Important viti- 

 eultural Investigations of the U. S. Department or Agriculture 



An investigation of the abnormal shedding of young fruits of the Wash- 

 ington navel orange, J. E. Coit and R. W. Horn. son (/ niv. ('"I. Pub*. Agr. >< »., 

 3 (1919), No. 11, pp. 283-368, pis. 18, figs. $>).-— Observations an< Imeata 



dealing with the excessive "June drop" of Washington navel oranges in o-r- 

 taln sections of California are reported. Most of the field experiments w< 

 conducted in Kern County in orchards situated to the leeward of a consider- 

 able stretch of desert, typical of the southern San Joaquin Valley, wher 

 from the annual heavy drop and the light crops borne, the navel orange matures 

 early and is of excellent quality. The problem was studied both from the 

 pathological and physiological standpoints. 



The shedding was found to constitute true abscission, Involving the separa- 

 tion of living cells along the plane of the middle lamellae. Of the stimuli in- 

 vestigated, two, a fungus, Alternaria citri, and climatic conditions are held 

 to be responsible for the abscission. "It is considered highly probable that a 

 certain varying percentage of the drop, occurring relatively late in the season, 

 is brought about by the stimulation of this fungus, which is also responsible 

 for a black rot of those infected fruits which remain on the trees to maturity. 

 This fungus is of very wide distribution and infection of the young fruits is 

 made possible through the peculiar structure of the navel orange. The amount 

 of infection is dependent upon weather conditions and the more or less fortui- 

 tous configuration of the navel ends of the young fruits. On account of the 

 peculiar manner of infection and the relatively small amount of shedding 

 due to the fungus, spraying will probably not pay for the labor and materials 

 involved. By far the greater part of the shedding, which occurs earlier in the 

 season, is due to a stimulus to abscission arising from daily water deficits in 

 the young developing fruits, resulting from the asperity of the climatic com- 

 plex to which the trees are subject. 



"The principal factor in causing these abnormal water deficits lies in the 

 fact that citrus trees are not adapted to withstanding the heavy water Loss 

 incident to the desert conditions under which they are grown. The amplitude 

 of stomatal movement is small and cuticular transportation very high. It is 

 further believed that under the prevalent clean cultivation practice the soil 

 temperatures during a part of the day are so high as to result in the Inhibition 

 of absorption at the very time of day that water loss by transpiration is 

 greatest. It has been found possible to modify climatic conditions in an orchard 

 SO as to set crops in every way comparable with those produced in much more 

 climatically favored citrus districts. Under these modified climatic conditio 

 the abnormal water relations referred to apparently do not occur. 



'• Practical means of amelioration lie in heavier and more frequent Irriga- 

 tion, the planting of intercrops, mulching with straw and other mat. rials, 

 protection by means of windbreaks, and a reduction of leaf area by modem 

 winter pruning. Measures of an anticipatory nature lie in the j<i !• Lous 

 selection of the site for the orchard with reference to its exposure, nearn< -- to 

 large irrigated bodies of land, and other features calculated to amelion 

 climatic conditions. Orchardists should be on the lookout for mutant strains 

 which are dry heat resistant and satisfactory in other features." 



