830 



fungus, above referred to, the pea-leaf; and the spawn of mushrooms 

 certain soils, &c. 



" 2. The parasite affects the tuber secondarily, and inoculates it 

 by direct contact. 



" 3. Although the fungus bears fruit and seed, yet its spawn is it- 

 self capable of indefinite reproduction, and destroys by encroach- 

 ment, and a specific inherent property. 



" 4. Tubers taken from the ground free from infection will not 

 necessarily become infected, nor the future plants and tubers. 



" 5. Assuming that the atmosphere always contains, diff'used through 

 it, these vegetable germs, but generally in a dormant state, then 

 either some atmospheric change congenial to their development may 

 be inferred, or some declension in the potato plant, the result of con- 

 tinual propagation from the original parent sets, the probability of 

 such a result being borne out by the declension of fruits propagated 

 from grafts whose original parent tree has consummated the period of 

 its existence — but observations on seedlings would assist in elucidat- 

 ing this point. 



" 6. The dry coat of a tuber is unfavourable to the growth of the 

 fungus, but if, with the assistance of moisture, it has become infected, 

 the disease will extend to the interior, although its surface be after- 

 wards kept dry. 



" 7. The most likely mode of preserving the plant for future crops 

 is by carefully separating the healthy from diseased tubers, and ap- 

 plying to their surface some substance, as lime, &c., in order to de- 

 stroy any part of the fungus which may accidentally have reached 

 them. 



" 8. It will be unadvisable to crop the ground extensively with 

 potatoes, especially the varieties which are commonly matured at a 

 late period of the year, until cautious trial and experience shall have 

 proved that the state of the atmosphere or the condition of the plant 

 are unfavourable to the luxuriancy of the fungus. 



" 9. This fungus appears peculiar to the potato plant. 



" Memorandum. — The leaf of the turnip is often extensively af- 

 fected with a fungus which is intimately allied to the potato fungus, 

 but its effect is evidently only partially injurious. 



" It has been stated that the tuber, although checked in its growth, 

 will, even if the leaves and stalks be cut down, mature itself in the 

 ground, but, with great deference to those who have advanced this 

 opinion, I venture to suggest that the healthy life and natural decay 



