Bitter Pit in Apples. 417 



tent hereditary, but gives no explanation or cure for the 

 disease itself. From the purely practical point of view the dis- 

 covery of a completely resistant stock is highly improbable, and 

 resistant varieties of cultivated plants very frequently have 

 the unfortunate peculiarity that they are economically unprolit- 

 able. 



SUMMARY. 



The ripe pulp cells of apples are more sensitive to various 

 poisons than any other known organisms, the limit of toxic 

 action in the case of mercuric chloride being with a concentra- 

 tion of 1 in 10,000,000,000. The sensitivity tO' poisons varies con- 

 siderably in different varieties, and the pulp cells on the shaded 

 side of an apple are more sensitive to poisons than on that 

 grown exposed fully to the sun. 



The cuticle and bloom of sound apples arie remarkably imper- 

 meable to poisonous solutions. Moderately dilute solutions of 

 metallic poisons penetrate through the breathing pores in suffi- 

 cient amount to produce bitter pits, and yet in such minute 

 quantities as to be incapable of detection, even by very delicate 

 chemical analysis. 



When the cuticle or bloom is removed penetration takes place 

 readily. Hence apples should never be wiped or polished until 

 just before they are eaten. Apples have a certain power of 

 accumulating mercury and similar poisons from extremely dilute 

 solutions, but nevertheless, mercuric chloride is poisonous to 

 the pulp cells of apples without any accumulation in concentra- 

 tions down to 1 per 100,000,000, and possibly even lower. Cop- 

 per is not quite so poisonous as mercury, and lead much less so, 

 while its action is also slower. 



Young apples are more easily penetrated by dissolved poisons 

 than old ones, but their pulp cells are much more resistant. 

 Hence a young apple may absorb sufficient poison to kill a por- 

 tion of its tissue when adult, without any immediate toxic effect 

 being shown. 



Food and other substances occurring normally in the soil may 

 exercise a toxic action when presented singly, but in mixuires 

 their individual poisonous action is decreased. 



The poisonous action of copper sulphate and other soluble 

 metallic poisons to apples, may be decreased by the addition of 



