NON-PARASITIC, OR PHYSIOLOGIC PLANT DISEASES 57 1 



volumes with plates and illustrations in which he presents the evidence 

 in favor of the hypothesis that the stippen is due to irregularities in the 

 factor influencing the balance between transpiration and water supply 

 and not to poisoning of cells, e.g., by arsenical sprays as supported by 

 abundant experimental proofs. He beheves that the principal contrib- 

 uting factors are: 



1. Intermittent weather conditions when the fruit is at a critical 

 period of growth. 



2. Amount and rapidity of transpiration. 



3. Sudden checking of the transpiration at night when the roots are 

 still active owing to the heat of the soil. 



4. Failures of supplies at the periphery of the fruit followed by 

 spasmodic and irregular recovery. 



5. Irregularity of growth, so that the vascular network controlling 

 the distribution of nutritive material is not formed regularly. 



6. Fluctuations in temperature when fruit is in store. 



7. Nature of the variety. 



Water-core of Apple.^ — The diseased fruits are characterized by 

 hard watery areas in the flesh, usually in the core and extending out- 

 ward. Occasionally the flesh is marked by scattered small spots with 

 extensive watery areas near the surface. The abnormal areas are 

 usually associated with the vascular tissues. The seed cavities contain 

 liquid and the hard partition membranes become cracked and covered 

 with the hair-like out-growth known as tufted carpels. Norton states 

 that the intercellular spaces so conspicuous in the normal apple 

 flesh are filled with fluid in the diseased tissue so that the white opaque 

 appearance of the normal flesh is lacking. "The occurrence of the 

 disease under conditions favoring excessive sap pressure or cell turgor, 

 on vigorous growing trees, or trees with the foliage reduced by blight, 

 and especially in late summer when the air is cold at night and the soil 

 warm, the cracks in the carpels, the occurrence along the vascular tissue, 

 the liquid filling the intercellular spaces, lead me to the conclusion that 

 the trouble is due to sap forced into the seed cavities and intercellular 

 spaces by excessive sap pressure under conditions of reduced transpira- 

 tion. The air being excluded from the inner cells by the liquid filling 

 the intercellular spaces, anaerobic respiration may be increased and 



^ Norton, J. B. S.: Water Core of Apple. Phytopathology i: 126-128, Aug., 

 1911. 



