8 



Mycologia 



of the central cylinder by the crown gall tissue appears. There is, 

 however, a. slight hyperplasia of the wood. The fan-shaped 

 vascular elements in the gall seem to be running into the branches 

 "Y" and "Z " from " X." The gall in this case may be* com- 

 pared to the so-called benign tumors (Levin and Levine, 1918). 

 The character of the tissue of this neoplasm does not differ from 

 that of a malignant crown gall. It seems obvious that the death 

 of the crown gall is in general a result of merely mechanical 

 conditions. The gall may be insufficiently supplied with food and 

 water and dies because it fails to establish an adequate connec- 

 tion with the conducting system of the host. It is most likely 

 that this is true of the almond crown gall described by Tourney. 



Bacterium tumefaciens from stem and crown gall. The possi- 

 bility that another organism as well as Bacterium tumefaciens is 

 present and is responsible for the destruction of the stem apex 

 as shown in figures 3, 5, 6 was tested in the following manner. 

 Small pieces of the interior of the crown gall shown in figures 3 

 and 6 were carefully removed with a sterile knife and placed in 

 tubes of beef agar. In two days the surfaces of the agar on 

 which the inocula were resting became covered with a hyaline, 

 whitish yellow colored schizomycete which in general appearance 

 is not unlike that of Bacterium tumefaciens. Similar results 

 were obtained by planting pieces of the stem from above the 

 crown gall after being superficially sterilized by immersing in a 

 weak formol solution. In all tubes the organisms were more or 

 less alike in their superficial appearance. In several beef agar 

 cultures the hyphae of a mold made their appearance. The 

 presence of the mold we consider accidental contamination. 

 Molds at any rate are not known to be parasitic on and to cause 

 death of the rubber tree. 



It appears from this that the organism is carried to parts re- 

 moved from the gall but owing to its depauperate condition is 

 unable to influence the production of a new growth. 



The organism obtained in these cultures were inoculated into 

 the tissue of young growing geranium plants and young shoots 

 of the rubber trees. Crown galls appeared within two months 

 after inoculation. The growths were much smaller than those 



