CONTRIBUTIONS FROM THE WISLEY LABORATORY. 



49 



known as black-leg, but the writer's experience inclines him to the 

 opinion that black-leg is, after all, frequently superadded, as it were, to 

 a physiological condition of the plants affected, which would find expres- 

 sion in some form of disease independent of the black-leg bacteria. 

 Another disease has been described by Miss Dale,* and the difficulty 

 which this investigator experienced in bringing about infection of the 

 potato plant is most noteworthy. Taking all these things inta con- 

 sideration, he is inclined to believe that the fundamental cause of 

 bruise is physiological. - 



If this be the case, it should be capable of being cured, and it is 

 perhaps possible to prevent its recurrence by altering or improving the 

 conditions of cultivation. The fact that the disease has been frequently 

 found in potatos attacked by wireworm on land only a short time brought 

 into cultivation supports this contention. 



Summary and Conclusions. 



The results obtained in this investigation may be summarized briefly 

 as follows : — 



1. The disease is found among a large number of varieties of potato. 

 It becomes unpleasantly evident somewhat late in the storage period. 



2. Diseased tubers, when planted under the circumstances 

 described, yielded a perfectly healthy crop. 



3. The disease has not been induced to spread from one tuber to 

 another. 



4. In areas of potato tissue newly affected with bruise, diseased and 

 not-diseased cells are interwoven. The earliest post-mortem change to 

 be observed in the diseased cell is merely one of altered refractive 

 index and protoplasmic movement which is evident in the adjoining 

 living cells can no longer be observed. 



5. A wound cambium is not formed between diseased and healthy 

 tissue, as in the case of tubers affected with internal disease, streak- 

 disease of PKytophthora. 



6. No hyphal organism has been observed either within the diseased 

 cells or the air-spaces. 



7. Bacteria have not been identified within or about newly killed 

 cells. 



8. The use of Mandelin's reaction and Brandt's reaction indicates a 

 comparatively greater quantity of the alkaloid-glucoside solanin in the 

 diseased than in the non-diseased tissue. 



9. It is suggested that bruise is fundamentally a physiological 

 disease. 



10. If this be the case it should be capable of being cured, and it is 

 perhaps possible to prevent its recurrence by altering or improving the 

 conditions of cultivation. S. F. Ashby, in an investigation relating to 

 the quality and composition of potatos, pointed out that the best 

 " came from soils which were neither lacking in the coarse particles 



* E. Dale. "A Bacterial Disease of Potato Leaves." Annals of Botany, 

 xxvi. (1912), p. 133. 



VOL. XXXVIII. E 



