THE POTATO ROT. 109 



In some places it is the custom to put dry earth in the pit among the pota- 

 toes. As both light and air favor the production of the fruiting branches of 

 the fungus this is probably a good thing. It is probably impossible for the 

 vegetative branches to pass in the pit from one tuber to another. In one case, 

 however, out of several where I fastened the cut surfaces of a sound and a dis- 

 •eased tuber together the threads of the fungus appeared, with all the marks of 

 the disease, in the previously sound tuber in a few days. 



7. Do varieties differ in their liability to this disease ? They undoubtedly 

 do. Early varieties are certainly most exempt. The Late Rose seems to be 

 •especially liable to attack, but with most varieties now in cultivation in this 

 country little has been observed in this respect; though of older sorts quite a 

 list might be given of varieties said to be especially liable to or especially 

 free from rot. We need careful observations on this point. It has been 

 thought that plants raised from seed would be less liable to attack than those 

 from tubers, but it has been proved that seedlings are often attacked, even the 

 first season, and nothing need be expect-d from the frequent introduction of 

 seedlings, except that some new varieties will likely be more liable than others 

 to the attack, from whicli the best can be selected. The mere fact of being a 

 seedling apparently makes no difference. 



8. The condition and location of the ground as to moisture is important, as 

 moisture favors the germination of the fungus and perhaps, its further devel- 

 opment in the jjlant. The soil should, therefore, be sandy or well drained. 

 All low, damp, or foggy locations should be avoided if rot is feared. Exposed 

 situations, where little dew is deposited, and that little soon dried by wind and sun, 

 ■are to be preferred. It is also evidently desirable to keep the crop as free from 

 weeds as possible, which shade the soil and retain surface moisture. For the 

 same reason wide planting is beneficial, and the growth of varieties with upright 

 and not too rank foliage. 



9. As the fungus lives over winter in the diseased tubers it is especially 

 important to plant none but what are sound. Seed potatoes should be obtained 

 from fields or localities known to be free from rot. Merely choosing appar- 

 ently sound ones from among others is not safe, as it is impossible to detect 

 slightly diseased tubers without cutting them up too much. Other advantages 

 from a change of seed may be obtained at the same time, and so make the 

 change desirable in cases where, from but a slight danger from rot, it would 

 not seem worth the trouble. 



10. Avoid planting on land where the crop has rotted the preceding year, 

 for though no part of the fungus is known to pass the winter except in living 

 tubers, spores capable of passing the winter may exist and be present in such 

 localities in old tops and decayed tubers. An undoubted danger on such land 

 is from volunteer plants from potatoes left in the soil. These should be 

 -destroyed as soon as they appear, for if they are from diseased tubers they 

 will almost certainly become diseased and infect others. 



CONCLUSION. 



These seem to be the most important remedies we now have. Others will 

 suggest themselves to one who considers the cause of the rot. None of these 

 can be depended on to completely eradicate the disease when once established, 

 and it is doubtful if we shall ever be entirely rid of it. The fungus has already 

 spread nearly everywhere that the potato is grown, though it is quite probable 

 that the exemption of some localities from attack may be due to the absence 

 of the fungus in that region at the time. 



