[Proc. Roy. Soc. Vjctoria, 30 (N.S.), Pt. I., 1917]. 

 Aki'. 111.— 7'Ae Cause oj Bitter Pit. 



By ALFRED J. EWART, D.Sc, Ph.D. 



(Professor of Botany and Plant Physiology in the Melbourne University, 

 and Government Botanist of Victoria). 



[Read loth May, 1917], 



In his fourth report upon this "disease," Mr. McAlpine in 

 .summing up refers the origin of Bitter Pit to two causes, lx>th 

 connected with the supply of water. 



The first cause is considered to be due to irregularities of growth, 

 the pulp growing more rapidly than the network of vessels, " so that 

 meshes here and there are not formed and the loss of water at these 

 spots cannot be fully met by a fresh inflow of sap. This causes 

 the cells to collapse, the sap reaches an injurious concentration, 

 causing the cells to die and turn l)rown." 



The second cause is supposed to be the exact opposite of this, 

 namely that an excess of water causes so great an increase in the 

 pressure within the cells that they rupture and die, producing the 

 characteristic appearance of Bitter Pit. 



In regard to the first cause, since it is a morphological change 

 readily capable of demonstration, one would expect to find some 

 evidence of its existence brought forward. No such evidence is 

 given in the whole of the voluminous reports. The statement is a 

 supposition of possibility not based upon actual observation, and 

 immediately contradicted by observed facts. Bitter Pit spots 

 occur both on and near vascular bundles with healthy cells existing 

 in the tissue further out supplied by the same bundles. Any 

 interruption of the vascular supply would naturally affect all the 

 tissue supplied by the bundles. In some cases a layer of bitter pit 

 tissue may spread over a square centimetre or more extent, and 

 crossing the course of a whole series of bundles. Nevertheless healthy 

 tissue supplied by the same bundles may exist beyond the affected 

 area, showing that the death of the affected cells cannot te due to an 

 interruption of the vascular supply. 



In regai'd to the .second cause, excess of water causing an increased 

 pressure bursting the pulp cells, it may be noted that the pres- 

 sure within the pulp cells depends upon the osmotic concentra- 

 tion of the cell-sap within them, and that an abundant supply of 

 water simply enables the full osmotic pressure to be exerted. In a 



