4 BACTERIA IN RELATION TO PLANT DISEASES. 
this publication indefinitely since the writer no longer has living cultures of some of these 
organisms. 
Troubles of other sorts have been encountered frequently and the reader would be 
surprised, no doubt, to know how difficult it has been to obtain exact information on some 
of these subjects. 
Some definite rule must govern the citation of literature when it is very abundant as in 
case of some of these diseases, e. g., potato rots and pear-blight. Purely agricultural or 
horticultural literature has not been cited in this monograph unless it has a direct bearing 
on questions under consideration. Many speculative writings have been excluded. For 
this reason literature on any given disease earlier than that definitely ascribing it to a 
bacterial origin is, as a rule, not cited. Any other rule would have led to an endless number 
of citations of very little worth. Perhaps not enough exclusions have been made. In this 
matter it has been thought best to err on the side of fullness. Probably also some papers 
have been overlooked since the literature is scattered through many languages. Occa- 
sionally a citation has been made simply to show geographical distribution. 
As mentioned in vol. I the writer considers it advisable to state whenever possible the 
exact temperatures at which experiments were made, but it happened frequently in the 
great mass of notes from which the following pages have been compiled, that the expression 
“room-temperature” is used. It may therefore be useful to certain readers to know that 
the Washington room-temperatures, 7. ¢., those of our laboratory, vary roughly as follows: 
Summer temperature 25° to 35° C., occasionally 38° to 40° C.; winter temperatures (heated 
rooms) 18°C. to 27° C., usually about 25° C.; spring and autumn approximately 20° to 25°C. 
While not averse to synthesis, the writer has usually followed the analytical method. 
In general, “‘lumping”’ things not known positively to belong together is a worse proclivity 
in natural history than excessive subdivision. Further experiments are often necessary, 
and until such time it is best to keep separate subjects not demonstrated to be identical, 
at least the writer has striven to follow this rule. The whole trend of modern scientific 
research is toward analysis of phenomena, and only in the later stages of knowledge do 
combinations come in properly to round out a subject throughly worked over. 
When one has to deal with many diseases some sort of nosology becomes necessary. 
That which appears to be most convenient for the purposes of this treatise is, first of all, 
the simple subdivision into three large groups: (1) the vascular diseases; (2) the parenchyma 
diseases without hyperplasia; and (3) cankers, tubercles, and tumors in which there is a 
more or less distinct hyperplasia. The reader should remember, however, that classifica- 
tions are only conveniences. 
There is marked bacterial occlusion of the vessels in those diseases which I have 
classed as vascular—occlusions so extensive as to render this feature of the disease most 
conspicuous, but it does not follow that there is not also some destruction of the paren- 
chyma. Vascular bundles are not on the surface of the plant, and some preliminary bac- 
terial destruction of the surrounding parenchyma must always occur before the disease 
can take on its true vascular character, except perhaps in those comparatively rare cases 
where the inoculation happens to be made directly into some bundle. Moreover, in later 
stages of these vascular diseases bacterial pockets of greater or less extent are often formed 
in the parenchyma, especially in its softer parts. The extent to which these closed cavities 
occur varies greatly in different diseases. In the brown-rot of potato and tomato they are 
numerous and often fuse into large tracts of disintegrated tissues (fig. 1). In Stewart’s 
disease of sweet-corn, on the contrary, they are neither very large nor very numerous. 
Exception, however, should be made of the inner husks where they are common. 
In the remaining groups of diseases, occurring with or without hyperplasia, it is not 
uncommon to find occlusion of some of the vessels, although the first and principal dis- 
turbance occurs in the parenchyma. As examples of this may be cited the basal stem-rot of 
