50 



I believe that Wallroth's opinion is erroneous. It is true we find 

 fungous formations upon the dead parts, but none that attack healthy 

 tissues. Many have objected to the view that scab is caused by adding 

 lime, marl, or dung to the soil, but when it comes to final definite re- 

 sults the reports vary in regard to secondary circumstances. For ex- 

 ample, one person says that scab made its appearance after the appli- 

 cation of mail, but that the greatest development of the disease did not 

 occur the first year, 1 during which the potatoes were perfectly healthy, 

 but that the disease steadily increased during the ten following years. 

 The same account claims that beets are similarly affected by marl. It 

 is interesting to note that where the marl was not used the potatoes 

 showed no seab. In Posnia, in the seventeenth century, marl was fre- 

 quently added to the loose soil of large estates for the purpose of raising 

 Medicago media. This was generally preceded by two crops of potatoes, 

 which were always marled. In spite of this, scab never made its ap- 

 pearance if the marl was drawn before winter and thoroughly mixed 

 with the soil. 2 The same experiment was recorded a year earlier in 

 Saxony in the Zeitschrift des landwirthsch. Centralvereins (p. 219). 



Ileiden :: reports a very thorough experiment at Pommritz in regard 

 to the use of lime. A piece of new land was given heavy applications 

 of lime (3,000 pounds per acre) six times between 1808 and 1878, and in 

 1S7S the land bore potatoes after a fresh application. The potatoes 

 when gathered were completely free from scab. It will be seen that in 

 this ground there was lime of different ages, from the fresh to that ten 

 years old, and no injury resulted. 



Contradictory as these results appear, they may nevertheless be har- 

 monized if the theory should be confirmed that the frequently-occurring 

 secondary action of lime may be the dangerous agent that causes the 

 death of the growing cork cells. Ileiden directs attention to the fact 

 that the ammonia already contained iu humus is set free by the lime ; 

 when a great deal of lime is employed and the soil is not at the time 

 able to absorb all the ammonia that is set free, a part of it will escape. 

 This surplus ammonia will be very apt to destroy the loose cork cells 

 within the lentieels and cause the cork formation to penetrate farther 

 into the tissues. The ammonia will become harmless only when oxi- 

 dized into nitric acid, and we have a positive statement fn this direc- 

 tion. Kraus-Triesdorf 4 mentions the experiments of Dr. Schreiner, who 

 found that scabby potatoes were very abundant in almost pure quartz 

 sand which had been manured with ashes, pulverized turf, and nitrogen in 

 the form of ammonia; bat when in the form of nitric acid no such effect 

 was produced. Quartzsand, without manuring, or with the ashes alone, 

 did n ot produce scabby tubers, even when mingled with turf. Iron filings, 



1 Landw. Zeit. !'. WesCphalen und Lippe, L864, p. 106. 



-Fiililino's Landwirthsch. Zeit., 1871, vol. 5, p. 3&t. 



'Algemeiue Hopfenzeifcuug, 1882, p. 295. 



'('. Kraus., Mechanik dor Knolleubildung. Fl«wa,, L877, i>. I&j. 



