THE MONTHLY BULLETIN. 203 



foimd on ssuj^ar heels. (6) Tlie knot or liall oL" tlie oJive is caused \)y a 

 distinct species of bacteria. In addition to these there are other aerial 

 galls on the twigs of several different kinds of trees, the cause of which 

 is not yet fully understood. Citrus trees occasionally have these aerial 

 galls, also eucalyptus seedlings have small knots that never causes any 

 serious injury. The galls of quince are not very well understood and 

 do not seriously harm the affected trees. There are also natural galls on 

 certain varieties of olives that should not be confused with that of 

 crown gall. Locust trees sometimes have large galls on the trunk which 

 probably are not the same as crown gall. 



BACTERIAL NATURE OF DISEASE. 



The cause of crown gall has been fully demonstrated to be a species 

 of bacteria by the name of Bacterium lumcfaciens, a tumor-forming 

 organism. The germs are extremely small and may live in the soil or 

 organic matter as sa])rophytes, and from there enter into the tissue of 

 living plants through some injury in the bark. Artificial galls have 

 been repeatedly made to develop by simply pricking the healthy bark 

 with a steel needle previously touched to a pure culture of the causal 

 organism. In the gall or tumor tissue comparatively few viable bac- 

 teria are present, and the microscope does not conclusively demonstrate 

 the cause of the trouble under ordinary histological methods. The 

 germs live inside the cells of the host, and, by the products produced 

 during their development, cause new cells to be formed with unusual 

 rapidity and in increased numbers. The abnormal tissue thus formed 

 shows cells with very thin walls and it is at first soft and often with no 

 well defined bark or epidermis. The germs can often spread through 

 the plant by the developing of a narrow portion of tissue into a tumor 

 strand. This strand is invisible externally, but from it secondary 

 tumors often develop. 



Strong evidence has been presented by Dr. Erwin F. Smith showing 

 many similar characteristics to exist between human tumors and those 

 of plants, but to present these would be outside the scope of this paper. 

 All attempts, however, to produce tumors on the lower animals, fishes, 

 frogs, by inoculating them with crown gall organism have been failures, 

 or at least uncertain in their results. It is, therefore, safe to conclude 

 that the organism causing plant gall tumors can not produce tumore in 

 animals. 



VIRULENCE OF THE ORGANISM. 



The crown gall organism, however, is a virulent i)lant parasite, and 

 is capable of producing galls in a large number of plants when placed in 

 their tissue by artificial inoculations. Galls have thus been produced 

 artificially en several kinds of trees upon which they have never been 

 found to occur naturally. The most interesting of these are the dif- 

 ferent species of citrus, as the orange, lemon and lime. Negative results 

 have always been secured from inoculating the avocado and the olive. 

 The fig and loquat are infected "only with difficulty. Often the inocula- 

 tions when made do not at once show positive gall formation, but may, 

 as in the quince, remain in a dormant condition. In our quince inocula- 

 tions the injury made by the puncture inoculations healed, and it was 

 nearly a year before the small gall-like formations appeared. These 

 eventually, however, grew into large galls. The condition of the tree 



