2IO DISEASE IN PLANTS. 



kill or injure trees by tightly winding round them. 

 If strong wire is twisted horizontally round a stem, 

 the growth in thickness of the latter causes the 

 trapping of the cortex and cambium, etc., between 

 the wire and the wood, and a ringing process 

 is set up in consequence of the death of the 

 compressed tissues. A callus then forms above 

 the wound, as in the case of true ringing by 

 means of a cut, and eventually bulges over the 

 upper side of the wire : in the course of years 

 this overgrowth may completely cover in the wire, 

 and, pressing on to the lower lip of the wound, 

 mav at length fuse with the cambium below. 

 Hereafter the thickening rings of wood are 

 continuous over the buried wire. The process 

 is obstructed by all the impediments referred to 

 in dealing with ringing, and of course the stem 

 thickens more above than below the wire. If 

 the sapwood is thin, and the bark is so thick 

 as to put great obstacles in the way of the 

 junction of the upper and lower cambiums, 

 death may result the tree is permanently 

 ringed. (See p. 201.) 



Spiral grooves are frequently met with where 

 Wood-bine or other woody climbers have twined 

 round a young stem or branch, the upper lip of 

 the groove always protruding more than the 

 lower. If a kink or a crossing of two plants 

 or branches of the twiner results in a complete 

 horizontal ring, the results are as in the above 

 cases of ringing and strangulation. Naturally 

 grooved walking sticks are often seen. 



