76 BOTANICAL GAZETTE [JULY 
It may be said that the beginning of the present work dates back to the 
discovery of gall-like outgrowths on the stems of the Paris daisy (Chrysan- 
themum frutescens) in 1904. It was not until 1906, after many unsuccessful 
trials, that an organism was isolated which when inoculated into sound plants 
caused the growth of galls similar to the ones from which the organism had 
been obtained. The organism was inoculated from pure cultures into many 
different plants, several hundred inoculations having been made. The results 
showed that on nearly all herbaceous plants tried, such as daisy, pyrethrum, 
tobacco, clover, cotton, sugar beet, hop, and others, galls were produced as a 
result of the inoculations. Inoculations into such woody plants as rose, 
grape, almond, poplar, and Persian walnut also gave galls, but with less 
frequency than the herbaceous plants. JInoculations on a number of other 
plants did not result in the formation of galls, although in some instances 
inoculations had been successful in other experiments with the same plants. 
Later, crown gall organisms were isolated from a large number of other plants, 
th woody and herbaceous, including the common nursery trees, as apple, 
peach, and poplar, which suffer most seriously from the crown gall, and such 
organisms were also capable of infecting a number of hosts besides the original 
one. The “hairy root” of apple, which has been more or less associated 
with crown gall in the minds of nurserymen, was found to be due to the same 
organism which when inoculated into other plants, as the sugar beet, for 
instance, gave galls with the characteristic hairy roots. The vast amount 
of evidence of this nature presented in the bulletin shows that the crown gall 
and similar tumors, and the hairy root disease of various plants, are due to 
bacteria, and that the organism of each kind of plant is capable of being 
inoculated at least into several other plants. The organisms from different 
sources, while similar in their general characteristics, show minor cultural 
differences. This behavior leads the authors to leave undecided the question 
whether the organisms constitute several species or a single species with several 
races. 
An interesting comparison is made between the crown gall outgrowths and 
animal tumors to which they show resemblance in growth and organization. 
This resemblance is carried still farther by the formation by the plant galls 
of metastases, which occur at some distance from the primary gall, but without 
the intervention of new infections. It is suggested that the metastases occur 
as a result of growths from the primary galls. 
Another important idea is brought out in a number of experiments which 
tend to show that plants acquire immunity to the crown gall organism as 4 
result of repeated inoculation. If the result of those experiments should be 
confirmed by future work, this would be the first instance of immunity in 
plants analogous to that in animals. 
This work has removed from the domain of speculation the cause of crown 
gall and kindred diseases affecting many plants. These diseases, in all their 
varied manifestations, are shown to be due to a common cause. The enormous 
