14 BULLETIN 1156, U. S. DEPARTMENT OF AGRICULTURE. 
ordinarily late in the season, usually not until September, but by 
setting out tomato seedlings in a wart-infested garden in August 
infection has been brought about on very young plants. Similarly 
infection has been produced on young plants grown in water cul- 
tures. The readiness with which infection may occur is influenced 
to a considerable extent by hilling up the soil about the plants, thus 
inducing growth activity in the buds of the covered part of the 
stem. Under these conditions tumors which are evidently mal- 
formed stems or leaves and sometimes reach 2 centimeters in diameter 
are produced. Kunkel and Orton 16 reported root infections also, 
a noteworthy case, since potato roots apparently never become 
infected. While an examination of Kunkel's preparations shows 
indubitable resting spores -of the wart pathogen in a considerably 
disorganized tissue, which is nevertheless of root topography, sub- 
sequent observations have not brought to light wart infections on 
tomato roots. In 1920 many of the tomatoes under test developed 
very striking lesions in the nature of fusiform swellings or pulvinate 
outgrowths of the cortex of the larger feeding roots at the base of the 
stalk. The smaller " brace roots'' springing from near the crown 
were not observed to be so infected. These lesions were at first 
regarded as being due to Synchytrium, but a microscopic examina- 
tion of them in the fresh state consistently failed to show recognizable 
stages in the life cycle of this pathogen. Fixed and embedded mate- 
rial disclosed the presence of extensive areas of infected host cells, 
resembling the figures given by Melhus 17 for infection of tomato 
and potato roots by powdery scab (Spongospora subterranea (Wallr.) 
Johnson). Veritable " krankheitsherde were commonly present, 
involving from a few to several hundred host cells in which each 
host nucleus was surrounded by a plasmodium or an aggregation 
of amoeba? containing numerous minute nuclei. The host nucleus was 
greatly enlarged, but appeared otherwise normal. The parasitic 
nuclei agreed in size with the figures of Melhus representing Spongo- 
spora; they possessed a definite nuclear membrane, a central 
nucleolus, and usually a few delicate chromatin strands. No division 
stages have as yet been made out in these nuclei, but there was 
clear evidence of giant host cells showing mitotic nuclear division 
which was not immediately followed by cell division. Neither have 
any stages suggesting spore ball formation in Spongospora as de- 
scribed by Osborn 18 been observed. A complete cytological inves- 
tigation of these galls is in progress; meantime, they are provisionally 
referred to Spongospora subterranea. It is noteworthy, however, 
that powdery scab affecting potatoes had not been reported from 
any part of Pennsylvania up to this time, but a careful search for 
its presence, made subsequent to finding these tomato-root infec- 
tions, disclosed its limited occurrence on certain English varieties 
growing in a different garden. 19 
i« Lyman, G. R., and others. Op. cit. 
» Melhus, I. E., Rosenbaum, J., and Schultz, E. S. Spongospora subterranea and Phoma tuberosa on 
the Irish potato. In Jour. Agr. Research, v. 7, pp. 213-254, 1 fig., pi. A (col.), 7-14. Literature cited, p. 
253. 1916. 
*• Osborn, T. O. B. Spongospora subterranea (Wallroth) Johnson. In Ann. Bot., vol. 25, pp. 327-341, 
pi. 27. Bibliography, p. 340. 1911. 
!» Shapovalov, Michael. " Skin spot. " a stage of powdery scab. (Abstract.) In Phytopathology, vol. 
12, pp. 37-38. 1922. 
