INVESTIGATIONS OF POTATO WART. 11 
hand and may be introduced into general culture. In particular, a 
potato is desired which shall combine immunity with the drought 
and heat resisting qualities and other desirable characters of the 
Rural New Yorker. * As the details of this study are of technical 
interest only and as a report has been issued which embodies the 
results attained to date ll reference to the seedling tests is here limited 
to the statement that immune seedlings having as one parent a Rural 
type are already at hand, but the testing of their commercial value as 
compared with standard varieties will be the work of several years. 
Meantime, new hybrids of similar origin will be sought, and all wart- 
immune seedlings will be subjected to careful tests of yielding capacity, 
general adaptability, and disease resistance, to the end that should 
any of them be brought into general culture their introduction will 
be a distinct gain over existing varieties. 
TESTS WITH MISCELLANEOUS SOLANACEOUS SPECIES. 
One of the favored theories to account for the origin of the wart, 
or at least its sudden appearance and rise to economic importance in 
Europe, has been that the pathogen has spread to the potato from 
some other host, which is believed to have been some native plant 
upon which it produced only inconspicuous malformations and hence 
was overlooked. In support of this hypothesis it has been shown 
that this disease appeared rather suddenly in England during the last 
decade of the nineteenth century. Although some earlier accounts 
antedating this by 20 years may have actually referred to the same mal- 
ady, nearly 150 years elapsed after the introduction of the potato into 
general culture in Europe before any mention of tins disease is found. 
Its slow extension during the next 10 or 15 years may have been due 
to the gradual adaptation of the parasite to a new host, upon which 
it ultimately came to have its present marked pathological effect, 
leading to its recognition. The rapid spread in the British Isles 
within recent years can be accounted for, as Taylor 12 has shown, by 
the introduction into general cultivation of susceptible potatoes, to- 
gether with the movement of seed stock, particularly from Scotland 
after the disease had become well established there. It seems un- 
likely that the wart pathogen was introduced into Europe along with 
the original potato, since some of the endemic species of Solanum of 
South America most closely related to Solanum tuberosum resist in- 
fection 12 (see note 15, Table 1), although if such immunity could 
have developed through long association with the pathogen this evi- 
dence is not significant. The comparatively recent appearance of 
this striking malady is better evidence against such early introduc- 
tion. On the other hand, Cotton 13 has found that the common gar- 
den weeds, Solanum nigrum L. and S. dulcamara L., are susceptible 
to infection by Synchytrium endobioticum (Schilb.) Perc, although 
they have never been found warted in nature. 
Although the biological validity of the theory which assumes that 
this parasite within recent times has passed over to a more congenial 
host may be open to serious objections, the importance from the 
11 Orton, C R., and Weiss, Freeman. Op. cit. 
11 Taylor, H. V. The distribution of wart disease. In Jour. Min. Agr. (Gt. Brit.), vol. 27, pp. 733-73S, 
863-867, 946-953. 1920-21. 
u Cotton, A. D. Host plants of Synchytrium endobioticum. In Roy. Gard. Kew. Bui. Misc. Inform., 
1916, pp. 272-275. 1916. 
