166 
yet possibly other factors are involved. 
Frequently the growth of the strand is 
rapid. In very juicy favorable material in 
16 days from the date of the primary inoc- 
ulation I have seen secondary tumors de- 
velop from such strands at a distance of 
10 centimeters from the parent tumor. 
Often deep in the resistant wood the tumor 
strand is under great pressure. In softer 
parts the overlying tissues are split open, 
and the deep secondary tumor then comes 
to the surface. In the Paris daisy, when 
the primary tumor is on the stem, second- 
ary tumors often develop on the leaves, 
and strands of tumor tissue have been 
traced in numerous instances all the way 
from the primary tumors through the stem 
into the leaf, and all stages of the develop- 
ment of the secondary tumors observed on 
many plants. This tumor strand boring 
its way through stems and leaves appears 
to be as much a foreign body as the roots 
of a mistletoe or the mycelium of a fungus. 
From these strands and from these second- 
ary tumors we have isolated the same 
microorganism that occurs in the primary 
tumors and with subcultures from such 
bacterial colonies have reproduced the dis- 
ease. The discovery of this strand affords 
a satisfactory explanation for the fact that 
the morbid growth usually returns after 
excision. 
The second striking fact to which I wish 
to call your attention is that when the 
primary tumor occurs in the stem and the 
secondary tumor in the leaf the structure 
of the secondary tumor is not that of the 
leaf in which it is growing, but of the stem 
from which the strand was derived. If the 
discovery. of the strand was an accident, 
this latter discovery was reasoned out, 
knowing what takes place in eancer. I 
_ said immediately, if this is a tumor-strand 
we ought to find a stem-strueture in the 
leaf tumors, and the very first leaf tumors 
SCIENCE 
[N.S. Vou. XXXV. No. 892 
cut showed typical examples of it. In 
secondary tumors occurring in the leaves 
as the result of stem inoculations the de- 
velopment of a stem consisting of a loose, 
rapidly growing parenchyma in the center, 
surrounded by wood wedges separated by 
medullary rays, beyond which is a cam- 
bium zone and a bark can be made out very 
clearly (slides exhibited). Sometimes 
these secondary tumors develop a very per- 
fect stem structure; often, however, the 
stem is more or less imperfect with the in- 
clusion of large parenchyma cells of the 
leaf, and with a great overproduction of 
stem parenchyma (medullary rays, etc.) 
as compared with the vascular portion. As 
this secondary tumor grows the surround- 
ing leaf structure is destroyed, and eventu- 
ally we may have a growth which bears no 
resemblance whatever to a leaf. Often, 
however, fragments of the leaf adhere to 
the surface of the tumor, and show an un- 
changed leaf structure. 
These secondary leaf-tumors then, so far 
at least as regards the parenchymatous 
portion, are composed, in great part at 
least, of descendants of the originally in- 
fected stem-cells. The growth is an in- 
vasion of infected cells. To what extent 
neighboring uninfected cells are also in- 
volved is uncertain. The wood always 
- shows hyperplasia, sometimes to a very 
marked degree in the vicinity of a stem 
tumor, and usually also in the vicinity of 
the tumor strand, especially if this is large. 
Are all of these wood cells infected? Prob- 
ably not. I see-no reason why we might 
not have changes in the plant distantly 
comparable to the inflammatory changes 
which take place in the vicinity of a. ma- 
lignant animal tumor, 7. e., an excessive 
multiplication of cells which while a part 
of the tumor are not its malignant portion. 
This must be left for further: study. ; 
This astonishing stem structure in leaves 
