1918] DISEASES OF PLANTS. 353 



IMany environmental factors contribute to the production of bitter pit. The 

 primary cause, however, is unqualifiedly stated to be the pressure of sap in the 

 outermost layer of pulp cells, which causes them to burst and also ruptures the 

 associated vascular network. This pressure is thus too great for the consti- 

 tutionally weakened tissue of the cultivated apple. The falling in of the sljin 

 is due to a deficiency in its nourishment and to the collapse of the underlying 

 cells. The browning of the tissue originates immediately beneath the skin, but 

 its extension along the conducting vessels may streak the flesh of the apple. 

 There may be also an internal browning not noticeable at the surface. Bitter 

 pit on the tree or in storage develops only in apples approaching maturity, never 

 after its attainment. The pitting is generally confined to the calyx end of the 

 fruit. There are both discrete and confluent forms of pitting. 



In the manurial experiments in Victoria, the smallest amount of pitting oc- 

 curred when bone dust was added to a complete fertilizer, high yield showing 

 but little effect on the disease. In New South Wales the highest yield was asso- 

 ciated with the least pitting, which was less than 0.5 per cent, but in South 

 Australia this condition was reversed. In Western Australia the least pitting 

 occurred where 1 lb. of iron sulphate was applied to each tree. Here also fer- 

 tilizers tended to increase pitting, but the opposite result appeared in New 

 South Wales, South Austi-alia, and Victoria. Excess of nitrogenous manures 

 tends to produce pitting on account of the rapid growth, accumulation of nu- 

 tritive substances, and imperfect cell development. 



Pruning is one of the most important means of control and has received spe- 

 cial attention. The best results have been obtained by leader or light pruning. 

 Whatever favors the regulation of the sap and its proportional distribution to 

 the various fruit buds, so that each is well supplied but not gorged, also tends 

 to reduce or prevent bitter pit. In a susceptible variety, such as Cleopatra, 

 pitting has been reduced to from 4 to 6 per cent by pruning. Storage at 30 to 

 32° F. arrests or retards both bitter pit and overripening, as the apple while at 

 this temperature is in a state described as a sort of suspended animation. 



Bitter pit: Its cause and control. Experiments in pruning', manuring, irri- 

 gation, cool storing, D. McAlpine {Fruit World Austral., 18 (1911), No. 4- PP- 

 92-96, 99, 103, figs. 3). — This is a brief account of the report above noted. 



Effect of temperature, aeration, and humidity on Jonathan spot and scald 

 of apples in storage, C. Brooks and J. S. Cooley (U. S. Dept. Agr., Jour. Agr. 

 Research, 11 (1917), No. 7, pp. 287-318, pis. 2, figs. 23).— A report is given of a 

 study of Jonathan spot and scald of apples in relation to rot Infection and 

 the modifying effects of storage conditions and maturity of fruit. Both of the 

 troubles are said to be important, not only because of their damaging effect 

 on the appearance of the fruit, but also because of the part they play in 

 paving the way for the entrance of various rot-producing fungi. 



These disea.ses are said to show many similarities. The initial stages of 

 both are found to be confined to the color-bearing cells of the skin ; both render 

 the apple susceptible to rot infections; both are decreased by good aeration 

 and a fair degree of maturity of the fruit; and both are increased by a rise 

 in temperature, having an optimum of about 20° C. and a maximum of 

 about 30°. 



The authors consider that apple scald is due to abnormal respiratory condi- 

 tions resulting from poor aeration. Attention is called to the important role 

 which aeration plays in the prevention of apple scald, as may be observed from 

 the small amount of this disease in cellar and air-cooled storage. 



Fire blight infection, H. A. Gossard and R. C. Walton (Mo. Bui. Ohio Sta., 

 2 (1911), No. 11, pp. 357-364, figs. 5).— The results are given of an Investigation 



