170 
actly as it does in the flask cultures, caus- 
ing them to take on involution forms and 
killing the majority. 
There is, as I conceive, a very delicate 
balance between the parasitic bacterium 
present in the plant and the activities of 
the plant cells. The cells of the plant are 
not destroyed by it, but only stimulated 
into rapid and repeated division. Upon 
its entrance into a cell, which must usually 
be by wounds, in our own experiments by 
needle-pricks, we may conceive the micro- 
organisms to multiply rapidly for a short 
time. The acid developed by this multipli- 
eation then inhibits the further growth of 
the bacteria, causing the appearance of Y- 
shaped bodies and the death of a certain 
proportion of the bacteria, sometimes 
nearly or quite all of them. The mem- 
brane of the bacterial cells which are killed 
is now permeable, and the bacterial endo- 
toxines diffuse out into the cell. The 
nucleus of the cell now immediately 
divides, under the stimulus either of the 
acid or of the aforesaid endo-toxines, or 
possibly from an excess of carbon dioxide 
due to the bacterial growth. There can be 
no doubt, I think, that carbon dioxide ex- 
ists in excess in these cells, because the 
erown-gall tissues contain an excess of 
chloroplasts in the absence of any other 
visible means of obtaining this necessary 
food. These chlorophyll bodies are so 
abundant. as often-to give a distinct green 
eolor to deep tissues wherein we would 
ordinarily expect to. find but few chloro- 
plasts. 
The next difficulty is to explain why the 
paralyzed bacteria carried over into the 
daughter cells suddenly begin a new 
growth. This can result, I think, only 
from the pouring out into the cell at the 
time of division of a fluid which was not 
previously present. init, namely, the nu- 
clear sap which must flood the cell as soon 
SCIENCE 
[N.S. Vou. XXXV. No. 892 
as the nuclear membrane’ disappears. 
Whatever the explanation may be, the 
bacteria take on a new growth for a short 
time in the daughter cells with the repro- 
duction of the already outlined phenom- 
ena. In this way occurs within a few 
weeks or months an enormous overgrowth 
of the tumor tissue with the development 
of strands and of secondary tumors as al- 
ready described. Using rapidly growing 
favorable plants, it is possible by means of 
a few needle-pricks carrying in the para- 
sitie organism to obtain a tumor as large 
as one’s fist in as short a period as ‘six 
weeks. Ordinarily, however, growth is 
slower. Dr. A. P. Matthews, to whom I. 
am indebted for suggestions respecting the 
effect of the nuclear sap on animal cells, 
tells me he has observed in ease of the en- 
trance of sperm cells into the eggs of star 
fish that the sperm retained its original 
form until the breaking up of the nuclear 
wall and the diffusion of the nuclear sap 
into the egg cell, whereupon the sperm took 
on'a rapid growth. 
Although we are able by means of 
poured-plate cultures to isolate the organ- 
ism in a pure state from young crown-galls 
and reproduce the disease at wall, we can 
not readily demonstrate the presence of the 
organism in the tissues by means of the 
microscope. If the bacteria were as read- 
ily seen in crown-gall tissues as they are, 
for instance, in the tuberculosis of the . 
olive, the cause of the disease would have 
been discovered long ago. The organism 
is not an acid-fast organism, and when it 
stains at all a great variety of cell inclu- . 
sions also stain and some of these derived 
from the cell protoplasm or from special 
parts of the nucleus are confusing. Its 
staining is also complicated by the fact of 
its passing over so readily into involution 
forms which are proverbially difficult to. 
stain. I have seen occasionally inside of 
