Levine: Studies on Plant Cancers 



3 



avoided and very often other parasitic and saprophytic fungi. In 

 this way and in such plants as Ficus elastica it is possible to show 

 definitely whether and in what degree the crown gall has an 

 injurious effect upon the adjacent normal tissue of the host. It 

 must be remembered however that while transportation of the 

 materials elaborated by the cancer cells of the animal is in some 

 degree limited, this is much more the case in plants. 



I have found some evidence of injurious effects spreading from 

 a gall upwards and finally killing the stem above the point of in- 

 oculation. This was the result in every case (10 branches) with 

 two exceptions. In the first the signs of death are only now, 14 

 months after inoculation were made, making their appearance. 

 In the other case described below, the stem, it appears, was cut 

 off for examination too soon. 



In no case was there any evidence that the death of the stem 

 above the gall was due to the obstruction of the sap flow or water 

 supply. Tourney's results do< not suggest the possibility of any 

 such direct mechanical disturbance on the part of the gall. I 

 will describe briefly a number of cases observed. 



Material and Observations. — Through the courtesy of Dr. S. 

 Wachsmann, director of the Montefiore Hospital, a number of 

 rubber trees (Ficus elastica) were placed at my disposal. These 

 plants were growing in large boxes and were kept indoors during 

 the winter months in a basement room well lighted and ventilated. 

 In the summer these plants were moved out on the campus of the 

 hospital. These plants make almost as much growth during the 

 winter as they do during the summer. Various parts of these 

 plants were inoculated with Bacterium tumefaciens, labeled and 

 then examined from time to time. It was found that within a 

 month indications of a crown gall made their appearance in the 

 part of the plant inoculated. 



Figure 1 represents one of the trees during the month of Janu- 

 ary used in this study. The terminal buds are opening and the 

 moderately green glistening apical leaves show evidence of an 

 active condition of growth. The plant shown in figure 1 with 

 five others of equal size were inoculated on July 28, 1919, by 

 pricking the tissue with a steel needle that had been previously 



