MASS-ACTION OF BACTERIA. pik 
cell-division; (2) the destructive action of antiseptic plant-substances, e. g., acids, before 
these can be neutralized or otherwise destroyed by the substances produced by the mul- 
tiplying bacteria.. 
In some instances, the introduction of a very considerable mass of bacteria seems to 
be necessary to induce disease; in other cases a very fewaresufficient. It would be extremely 
interesting to know the minimum number capable in any given case of inducing disease. 
This could be determined easily by the dilution method, and still more readily and with 
Fig 21." Fig. 22 
absolute accuracy by the use of Barber’s apparatus, but no one seems to have made any 
exact experiments. Good organisms for experimental purposes would be Bacillus phytoph- 
thorus, Bacillus tracheiphilus, Bacillus amylovorus, and Bacterium campestre, care being 
taken, of course, to select sensitive varieties and susceptible tissues, and to have all other 
factors comparable. 
SECONDARY TUMORS AND METASTASIS. 
Secondary foci of overgrowth occur in the olive and in the daisy as the result of internal 
infection. The writer has obtained them frequently in both plants by pure culture inocula- 
tions (plates 6 and 7, and fig. 23). The organisms pass through the tissues of the stems or 
leaves and set up irritations which lead to hyperplasias in particular spots in the deeper tis- 
sues. These tissue enlargements, later on, break through to the surface. Sometimes these 
secondary growths arise at a considerable distance from the primary tubercle. In case of 
olives inoculated in 1910 the writer observed numerous deep tubercles develop at a distance 
of 1, 2, and 3 feet from the point of inoculation within a period of 7 months in actively 
‘growing plants, both down and up the shoot. The movement is more apt to be up the stem 
or leaf, 7. e., with the transpiration current, than down the stem. 
In the olive a distinct channel of infection is traceable from the primary to the sec- 
ondary tubercle. This is usually (so far as observed) a narrow pathway in some part of the 
inner wood, the tissues being more or less stained and disorganized, and the bacteria present 
in abundance and easily demonstrable without staining. Whether similar downward 
*Fic. 21.—Three figures from Peirce’s paper: 
(1) Two root-hairs of Bur clover infected by nodule bacteria, showing characteristic bending at point 
of infection. x 50. 
(2) The lower of two root-hairs in 1, showing mass of bacteria in concavity of coil and infection thread 
running from this point through the hair. x 300. 
(3) Another infected and coiled root-hair, infection thread growing close to nucleus of hair. x 300. 
tFic. 22.—Two figures from Peirce’s paper on Root Tubercles of Bur Clover: 
(10) Section of a tubercle near meristem. Direction in which meristem lies is indicated by arrow. Section 
stained by Fleming’s triple stain and differentiated, after anilin gentian violet, by Gram’s iodine. Course of 
infection threads is definitely toward tubercle-meristem and generally toward nucleus of cell entered. x 200. 
(11) Onecell from 10, showing solid infection strand (zoogloeae) in which separate bacteria can be dis- 
tinguished. x 1000. . 
