Mr. Crum on the Potato Diseaxe. 91 



present year, has been already made known by Professor Kiitzing, a 

 German physiologist, who describes the so-called dry rot of former seasons, 

 as a disease in which the starch granules are so altered as to exhibit 

 minute brown fungi, previous to the destruction of the cellular tissue ; 

 whereas at present the cells become destroyed, while the starch granules 

 remain entire. On account of this peculiarity he has given to the existing 

 disease the name of cell rot. In the short time during which I have 

 been occupied with this subject, I have not been able to verify under the 

 microscope, these observations on the structure of the cellular tissue, from 

 the difficulty, perhaps, of obtaining thin enough perfect sections of the 

 substance. Professor Kiitzing attributes the effects he describes to the 

 weakness of the parts, occasioned by the too rapid growth of the tubers, 

 and tho absorption of too much water, which render the formation of a 

 strong and durable cellular membrane impossible. But on making the 

 experiment, I have not been able to find that the quantity of water con- 

 tained in a perfectly healthy potato is less than in one liable to the disease. 

 I rasped down very fine white potatoes, from a moderate crop, grown on 

 poor land with but little manure ; and having put a pound of the pulp 

 into a bag, and squeezed it firmly with the hand, I obtained from it 59 

 per cent, of juice. A red potato from the same field, and equally 

 unaffected with the disease, yielded 58 per cent. Another red potato, 

 itself sound, but from a field which had been well manured, and which 

 was much affected with the disease, gave 58J. In another experiment, 

 where the juice was pressed out and the solid part dried, the fine white 

 potato left 21*1 per cent, of solid matter, and a portion of a diseased 

 potato left 20*79 per cent. There is, therefore, no difference in the 

 quantity of water. 



I shall not trouble the Society with any speculations of my own as to 

 the manner in which this rupture of the potato may have been effected. 

 The subject is surrounded with difficulties, and much close investigation 

 is wanted to learn the circumstances which attend it. If the statements 

 now made are correct, we shall find that fungi are not the cause, but a 

 consequence of the disease in question, and our attention will be directed 

 to prevent the formation in the potato, of a soil in which the fungus always 

 fructifies, rather than to the parasite itself, of whose existence we should 

 be ignorant without it. 



Mr. Alexander Anderson exhibited turnips affected with the same dis- 

 ease, from a farm on the Ardincaple estate. 



3d December, 1845. — The President in the Chair. 



The following gentlemen were admitted members of the Society : 



Messrs. George Harvey, Andrew Risk, Moses Hunter, J. A. Hutchisn, 

 James Shanks, C. E., David Cunningham. 



