Levine: Studies on Plant Cancers 



5 



but cross and longitudinal sections of this gall made much later 

 showed this assumption to be incorrect as is further described 

 below. It is obvious at once however that there is some other 

 cause of death than the cutting of the water supply, since in that 

 case, the dying would progress from the tip downward. 



Twelve months after inoculation. Figure 3 represents the 

 same branch shown in figure 2 on December, 1919, approximately 

 12 months after the inoculation had been made. The crown gall 

 has almost girdled the stem encircling J4, of the stem's circumfer- 

 ence. The leaves above the crown gall have turned black and 

 fallen off while those below are turning a yellowish brown. The 

 major portion of the stem above the gall is dead, the injury pro- 

 gressing from the gall upward so that at the time the photograph 

 was made the top of the stem (Fig. 3) was still green and showed 

 indications of being alive. A cross section through the middle of 

 this crown gall appears in figure 4 and shows that the crown gall 

 tissue has become fully differentiated and thus further supports 

 the contention of Tourney and Hedgcock that the crown gall 

 growths are annual and Levin and Levine's views that these 

 growths are unlike animal cancers in that they are limited in 

 growth and become differentiated. The wood fibers and par- 

 enchymatous cells of which the crown gall is composed are dark 

 brown on the interior of the gall as they are on the surface. The 

 vascular elements are distorted and nodular on the periphery of 

 the tumor where their antecedents were undoubtedly centers of 

 rapid cell division before they became differentiated and old. 



Approximately one half of the original cylinder made by the 

 fibrovascular bundles is destroyed and replaced by crown gall 

 tissue. The tissue in the center of the crown gall is dark in 

 color, watery and is apparently disintegrating. The remaining 

 half of the wood cylinder appears to be undistributed and un- 

 doubtedly is mechanically fit to carry sap, as evidenced by the 

 still turgid condition of the top of the branch as shown in figure 

 5. This figure represents a longitudinal section of the upper 

 part of the stem including the upper part of the crown gall. 

 There appears to be only a partial destruction of the wood fibers 

 in the region of the stem occupied by the lesion as seen in the 



