524 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8, 
a large swelling, apparently a crown gall, while in larch, hemlock, and blue 
spruce this organism produces blighting of the leaves and no galls. 
Crown gall belongs in the great class of diseases involving hypertrophies 
and hyperplasias of the host tissue. The reaction of the host to the parasite 
in these cases is obvious and specific. In sharp contrast with these we 
have the great group of cases in which plants parasitized by fungous or 
bacterial parasites show susceptibility by lack of visible reaction. Their 
tissues become necrotic because of destruction by the invading parasite. 
Whether in the cases of crown gall, potato wart, club root, and many other 
diseases the reaction appearing in the form of neoplastic growths may be 
interpreted as actively protective, is a difficult question. The types of 
disease in the two cases are certainly sharply distinct in plants; the symp- 
toms in the former indicating accelerated metabolic activity and growth, 
while in the second case we have necrosis such as the soft rots, dry rots, 
cankers, etc. 
We need not accept the conception advanced by some plant pathologists 
that the better the health of the organism the greater the susceptibility to 
an invading parasite. Susceptibility implies a certain relative adaptation 
to serve as a substratum foi the growth of the parasite. The data presented 
as to crown galls on beets do not bear on the question of susceptibility. 
Under the conditions described the beets all showed practically icq percent 
susceptibility. It is, however, in my opinion clearly shown from the results 
described above that the invading parasite induces a visible reaction in 
direct proportion to the general health of the individual. The proliferation 
of cells in the region of the invasion depends upon the general vigor and 
capacity for growth of the host tissue. This is in marked contrast with those 
plant diseases in which disintegration of the tissues is the first obvious 
evidence of the presence of the parasitic germ. 
Summary 
1. Beta vulgaris, varieties Early Model, Egyptian Early, and Giant Man- 
gel Wurzel, were grown in different kinds of soil to test the effect of the soils 
on the growth, size, and weight of the root when artificially inoculated 
with Bacterium tumefaciens. 
2. Of pot cultures with (i) garden soil with an abundance of manure, 
(2) brown silt loam and manure, (3) brown silt loam, and (4) medium sand, 
the largest average weight of plants was obtained in the garden soil. The 
crown galls were also the largest on these plants. The plants grown in 
sand weighed the least, were the smallest in size, and had the smallest 
crown galls. 
3. Beets grown in open-air plots gave the same results. Those on the 
better soil were larger and heavier, and the crown galls on these roots were 
larger than those on beets grown in the poorer soil. 
4. While the weight of the individual plants both inoculated and unin- 
