223 
Oct. 3o f 1916 Spongospora subterranea and Phoma tuberosa 
esculentum, no spore balls could be found even after the plants had been 
killed by frost. 
The other four hosts did not do as well as Lycopersicon esculentum and 
Solanum warscewiczii, but their root systems were quite extensive and 
showed numerous galls having superficial characteristics common to 
those in the potato and tomato. The phloem was vigorously attacked 
by the parasite, which caused the xylem and vessels to be twisted out 
of their normal course in many instances, and the cells of the phloem 
were hypertrophied and contained a considerable quantity of starch 
grains. 
The most significant fact brought out in these tests is that infection 
took place in the root system of the tomato, and this is important in 
view of the fact that the tomato, is very extensively grown in the United 
States, and often on land used for potatoes. The roots are very gener¬ 
ally infected and the distortions and malformations more conspicuous 
and destructive than those on the potato (PI. 7, fig. C, D). 
When Spongospora subterranea was found to thrive on hosts other 
than the potato, examinations were made of the root systems of weeds 
common in and about potato fields, including members of the Cruciferae, 
Labiatae, Scrophulariaceae, and many other families, and also of culti¬ 
vated plants, such as clover, oats, wheat, and barley; but in no case 
were signs of infection found. No wild species of Solanum were found 
growing as a weed in the potato fields or in vacant lots near by. 
• HISTOLOGY OF THE GALLS 
The galls on the roots of the potato are simple in structure and may be 
termed kataplasmatic galls (PI. 7, fig. C, D). The funghs or exciting 
agent flourishes only in the phloem or meristematic tissue (PI. 8, fig. A), 
as explained by Woronin (17) in the case of rootlets of cabbage seedlings. 
Occasionally amebse are seen in the xylem, but they have never been 
found to be numerous ofi to show any signs of stimulating the cells to 
further growth. The plasmodium of the fungus enters the cell and causes 
marked hypertrophy, which distends the cell until it is from 80 to 140/i 
in length. Later this divides by cross walls until instead of one large 
cell there may be as many as six normal-sized cells, all of which have a 
nucleus and are surrounded by a goodly number of amebse, which would 
indicate that there is some sort of reaction between these bodies. Occa¬ 
sionally, however, one or more of the amebae are distantly removed from 
the host nucleus. As the gall enlarges, this hyperplastic growth of the 
phloem tissues often pushes the vascular system out of its normal posi¬ 
tion. The infected cells always contain numerous large and small starch 
grains, which do not wholly disappear until the spore balls are mature. 
Osborn (11) claimed that the fungus feeds on starch; but were this the 
case, such an abundant supply would not always be present. It seems 
clear, however, that the fungus stimulates the protoplast to produce 
