6o6 



Tlie main (|ueslion is, in what way can the first radial ckava<j;c have 

 taken place. And the only answer to this can be ; as the result of frost. 

 For we again iind here the browning of the pith crown, the tearing and 

 widening of the medullar}- rays, the phenomena of elevation and cleavage 



of the tissue which I have been 

 able to i)roduce experimentally 

 b}- the action of artificial frost. 

 CJnly. I ha\e not been able to 

 produce artificially the secondary 

 phenomena, viz.. the luxuriant 

 tissue increase. This probably 

 is based upon the fact that in 

 using artificial frosts I have not 

 yet found the proper juvenile 

 developmental condition. This 

 must be the time when the cam- 

 bial activity has just begun, as is 

 evident from the small number 

 of cell la}ers just formed by the 

 new annual ring. If the dis- 

 turbances occur later, capacity 

 for reaction in the tissue is less 

 and the excrescent cell increase 

 does not take place. Ciothe's ex- 

 periments show how very deter- 

 minative the time of injury is. 

 As already mentioned, he pro- 

 duced excrescences resembling 

 the canker of the grape, by a 

 continued tapping of the grape- 

 \ ine in the early spring. The 

 grape canker is closely related 

 ontogenetically to the canker of 

 the rose. 



g. Canki:k of the 

 Blackberry. 



It is a noteworthy fact that, 

 with the exception of grape 

 canker, all the other canker ev- 

 er esc enees are fuiind in the family of the Rosaeeae. In the canker of the 

 blackberry, cauliflower-like, hard, glistening, white tissue masses with a 

 beaded warty surface are produced on the older wood (cf.Fig. 144 k). 

 These tissue masses sometimes form isolated spheres ; sometimes collect in 

 elongated, wart-like cushions, as in Spiraea. The region of the eye is the 



Fig 



Uln'i-ry. 



