417 



;iii()llicr, csjiocially if lirnisod, cut, or brolccii. T!/is Inst .suj^^jcsts ii fiirtlier itrccautioii 

 (tl Ijandliiiji and iiiairiuy Ibe roots as litllo as possible. 



liUick rot is caused by a mold that, may iMiter the .si>rout from tlio motlier root in 

 Ilu3 hot-bod and thus transmit the trouble to the i)ot"xtoes of the next ^feneration. 

 It is also possible for the germs to remain for a considerable time in the soil, and the 

 rot to enter the roots directly therefrom. When once in the potato, it spreads through 

 It, embittering and bhickening the tissue until the whole root is worthless. The 

 gn^-itest 'precautions should be taken that only healthy roots are used in the hot-bed, 

 and that all sprouts showing any signs of blackening of stem or young leaves be 

 discarded. Field experiments in the future may lead to a direct remedy that may 

 be applied to the plants or the soil, or both. 



Soil rot is duo to the invasion of a fungous growth that attacks the roots through 

 their small lateral librils, usually when quite young, and not being able to spread 

 throughout the whole root, the further development of the infested potato may cause 

 a ]):irtial obliteration of the disease. Plants badly attacked are not able to i)roduce 

 vigorous vines, and the roots, while often numerous, are mostly small and unmarket- 

 able. The fungus produces vast numbers of spores in the diseased tissue, and this 

 becoming dry and powdery, the germs are largely left in the soil, where they probably 

 retain their vitality for a long time, and serve to inoculate the roots of the first sweet- 

 potato plants that are set upon the infested soil. The use of healthy sprouts does not 

 insure the crop from the fungus, and therefore remedy must be sought in ridding the 

 soil of the germs or preventing them from entering the young roots. The growing 

 of other crops upon an infested soil for a term of years, while at a present comparative 

 loss, is one of the most practicable methods of clearing the land. It is possible that 

 the fungus feeds upon other plants than the sweet-potato — a condition of things sus- 

 pected from an examination of the roots of several weeds growing among the potatoes. 

 Further field expernnents need to be made before deftnite results as to application of 

 remedies to the soil can be recommended. 



Stem rot. — Upon this the investigations were begun too late to obtain the first stages 

 of tlie disease. Several kinds of fungous growths have been met with, one or more 

 of which may have been the cause. The young roots begin to decay near the top, 

 the rot descending usually for only an inch or so, during which time new sprouts grow 

 from below, but to no purpose. 



Whitv rot is associated with a blue mold that, beginning at the base of fine hairs, 

 inoduces small but slowly deepening and broadening pits, until the whole root may 

 be changed into a dry, chalky, worthless substance. As yet this form of rot is not 

 oominon. 



Drii rot is another decay of the " sweets " of fungous origin, in this case not chang- 

 ing the exterior color, but transforming the substance into a dry, yellowish mass, 

 with ]iiv.)ples upon the surface, in which the spores of the parasite are jiroduced in 

 great numbers. Fortunately this trouble is as yet not serious. 



Scurf is a well-known superficial appearance of the potato, due to a dark mold 

 that grows in the surface cells of the root, and afterwards sends up dark spore-bear- 

 ing stalks. While reducing the market value of the potato the mold does not cause 

 a destruction of the root, and therefore is not an occasi<ui for any alarm. 



Leaf Might is the name of a trouble due to a fungus that confines its work to the 

 leaves, where it produces dead spots in the foliage, and thereby weakens the plant 

 to an extent proportional to the amount of spotting. 



White mold is more troublesome in New Jersey than the leaf blight, as it ruins the 

 older leaves, which turn brown and die. It, however, in contrast with soil, black 

 and soft rots, is a comparati lely harmless enemy. 



