The Cause of Bitter Fit. 19 



on a larger scale over at least 2 years, and on trees whose previous 

 history was known. 



The present position in regard to the theories of the origin of 

 bitter pit may therefore be summed up as follows : — 



(1) The bursting cell theory is founded on a confusion between 

 cause and effect. The cracks in the cell walls sometimes seen in 

 sections of dead bitter pit tissue are either cracks caused after death 

 by drying and contraction, or more usually are tears produced by 

 the razor. In sections cut from tissue imbedded in paraffin the 

 cracks are rarely seen, and are often entirely absent. 



(2) The vascular interruption theory is unsupported by any 

 morphological evidence, and is contradicted by direct evidence such 

 as the existence of healthy tissue beyond bitter pit areas where 

 according to the theory vascular interruption should have occurred, 

 Further, the occurrence of starch in the cells shows that the channels 

 along which carbohydrates are conveyed to the bitter pit tissue 

 must have been open and functioning freely. 



(3) The poisoning tlieory lias behind it the weight of the following 

 evidence : — 



Every symptom of this defect can be produced by the artificial 

 application of poisons, including the presence of starch grains in 

 dead cells. 



Various observers have noted similar results in leaves and young 

 stems as the result of the application of poisonous sprays (patclies 

 of dead tissue with In-own shrivelled cells packed with starch.) In 

 apples the sensitivity is so great that the poisoning may be oligo- 

 dynamic, i.e., poisoning may occur in the presence of traces of 

 poison beyond detection by ordinary chemical analysis. 



As apples ripen the sensitivity of the pulp cells to poison in- 

 creases, so that an apparently sound apple may develop bitter pit 

 after it has been picked. 



There is a close correspondence between resistance to poison and 

 resistance to bitter pit. The most resistant variety to bitter pit 

 (Yates) is also the most resistant to poison. Varieties specially 

 sensitive to poison are also specially sensitive to bitter pit. There 

 is also a close correspondence in regard to temperature effects. At 

 low temperatures the development of bitter pit is checked or retarded. 

 Similarly at low temperatures the resistance to poisons is greatly 

 increased, being 10 to 100 times greater at 0°C what it is at 2.5^C. 



Further, there is evidence to show that where a comparison is 

 possible the incidence of bitter pit is greater in orchards that have 



3a 



