OF THE EASTERN UNITED STATES 371 



Five seedlings of M. cerifera, which the writer had previously grown 

 from seed in the University of Pennsylvania greenhouse, were then 

 removed from the soil and their root systems loosened from adhering 

 sand by gently washing in clean water. With the aid of Mr. Lambert, 

 of the University Gardens, who, Uke the writer took special care to insure 

 against sources of infection by other organisms, the root systems were 

 one by one quickly dipped into 1:1000 corrosive sublimate solution and 

 then washed in sterile distilled water. While Mr. Lambert, with sterile 

 hands, held each seedling so treated, the writer, by means of a long needle, 

 previously sterilized by passing through the bunsen flame, removed a 

 small portion of the Actinomyces culture from one of the tubes and pricked 

 it into the root of 4 seedlings, marking the place of inoculation by tying 

 a sterilized piece of cord just above the puncture. The last seedling was 

 treated similarly -to the first four, with the exception that it was merely 

 pricked with a sterile needle. This served as a control. Each seedling 

 was then planted in a sterile pot containing sterile sand. Both pot and 

 sand were previously sterilized in the hot air oven at a temperature of 

 210° C. for 8 hours. The potted seedlings were then placed in a special 

 case in the greenhouse and daily watered with sterile Knop's solution. 

 At the expiration of 9 weeks the seedlings were carefully removed, washed 

 in clean water and their roots examined for the presence of tubercles. 

 These were found in a primitive state at the points of inoculation on all 

 but two including the control, which was pricked with a sterile needle 

 only Thin hand sections of one of the tubercles revealed the presence 

 of Actinomyces in the same condition as observed in the cells of the 

 tubercles of the M. cerifera seedling, as well as of the tubercles on the 

 other species above noted. The appearance of the infesting Actinomyces 

 within the cells of the host plants will be treated under the caption dealing 

 with the histology of the tubercles. 



Gross Structure of Tubercles 



The writer has found tubercles on the M. cerifera, M. Carolinensis, 

 and M. Macfarlanei seedling primary roots of 5 to 6 months' growth, and 

 from thence onward on the secondary roots inserted on the hypocotyl 

 axis, on nearly all the adventitious roots of subterranean branches and 

 on the subterranean branches of M. cerifera, M. Carolinensis, M. Gale, 

 M. Macfarlanei, and Coniptonia asplenifolia. 



The tubercles occur either singly, as is frequently the case on sub- 

 terranean branches, in small groups the size of a pea, or in larger coralloid 

 loose or compact clusters which frequently attain the size of a large 



