;^68 Alfred J. Eivavt : 



orchards, and showed that appearances resembling bitter pit 

 could be produced by various poisons. Curiously enough this 

 theory, although the first one based upon any experimental 

 evidence as distinguished from obser^-ational and imaginative 

 evidence, met with strong disapproval, and has popularly been 

 supposed to be entirely discredited. In the pre-ent paper I 

 hope to be able to bring forward conclusive proof of the poison- 

 ing theory of bitter pit, and also to show that it is not necessary 

 to withdraw or modify any part of Dr. White's paper, except in 

 so far as her tentative theory, that the source of jDoisoning 

 might be from poisonous sprays, only holds good partly, for 

 bitter pit may also occur in orchards which have never been 

 sprayed with poisonous compounds, although so far as the evi- 

 dence goes, it appears to be much less common in such cases. 



Obviously the first point of attack was to determine accu- 

 rately the specific resistance of apples to different poisons. 

 Extraordinary variations are shown in this respect by different 

 plants. Thus among the lower organisms w^e have Spirogyra 

 which is sensitive to concentrations of copper sulphate down to 

 1 part in 100 million of water, and the green mould, Penicil- 

 lium, which can grow and thrive on fifteen to twenty per cent, 

 solutions of the same poison. 0. Richter (Die Ernahiung der 

 Algen) has showm that coins placed in mere contact with diatom 

 cultures on agar, exercise a marked deleterious influence upon the 

 growth of these organisms, although the coins do not lose ap- 

 preciably in weight. Between these extremes intermediate 

 grades are known, according to the specific resistance of the 

 particular plant protoplasm, and whether it has or has not 

 the power of preventing the penetration of the poison into its 

 living substance. 



Part I. 



The Sensitivity of Apples to Poi.^ons. 



The majority of the apples used for these experiments were 

 special ones, mainly selected ones grown in an orchard rented 

 by me, unsprayed, and kept in the cool stores for one to five 

 months until needed. They included the following varieties: — 

 Jonathans, Yates' Pippin, Rokewood, Rome Beauty, Scarlet Non- 



