404 Alfred J, Evxtrt: 



sary to poison the pulp cells was reached, which Avould in this case 

 be at points under or near to the breathing pores or to the 

 centre of the fruit. 



Part II. 

 The Problem of Bitter Pit. 



According- to C. P. Lounsbury (Agricultural Journal, Cape of 

 Good Hope, 1910, page 150), this disease is a physiological one. 

 The spots develop while the apples are on the trees, and also in 

 apparently healthy fruit after storage. Certain varieties are 

 more immune, particularly those from colonial seedlings. Hence 

 he considers that by the selection of resistant varieties, the 

 disease may be partly controlled. 



I. B. P. Evans (Transvaal Department of Agriculture, Techni- 

 cal Bulletin I.) found that all imported varieties were more or 

 less subject to this disease, but that two native seedlings were 

 practically immune. The spots arise in close connection with 

 the vascular bundles where the excess pressure birrsts the pulp 

 cells. The oxygen with the enzymes acts on the tannin, pro- 

 ducing dark coloured oxy-compounds, and drastic action is 

 inhibited. The bursting pressure is produced during the night 

 stoppage of transpiration. 



Cases of cells bursting during development are known to 

 occur with pollen tubes and root hairs, but only when grown 

 under abnormal artificial conditions, and here we are dealing 

 with unicellular structures. Pole-Evans has overlooked the fact 

 that in the pulp cells of the apple we have a tissue in which the 

 cell walls press against each other, and hence are under com- 

 pression instead of tension at the points of contact. Further, a 

 localised increase of pressure by distending the walls would 

 diminish or obliterate the air spaces, and bursting would only 

 occur when the breaking strain was reached before the expan- 

 sion was completed. In plant tissues this appears only to 

 occur when preceded by a softening of the cell wall, of which 

 there is no sign in bitter pit. 



Further, puncturing young apples and half-grown apples on 

 the tree with fine sterilised needles so as to rupture some of the 

 pulp cells, may result in the production of flat or crater-shaped 



