44 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



respectively, the common holly giving us a fairly 

 medium breadth. 



In some cases, and markedly so in the oaks, there 

 are two kinds of medullary rays : large broad obvious 

 ones, with more numerous finer ones between them. 

 Such rays may also be distinguished as consisting of 

 many or one series of cells pluri-seriate and uni- 

 seriate medullary rays. In some Conifers a resin- 

 canal often occurs in the medullary ray : in the beech 

 the broad rays widen out where they cross the 

 boundary between the annual rings : in the hornbeam 

 the so-called broad medullary rays are composed of 

 several rays running parallel and close together. 



The next general character I have to consider is 

 that afforded by the presence or absence, &c. of the 

 so-called " annual rings." It may be, and has been 

 questioned whether zones indicating periodic changes 

 in increment are ever absent from the timber of trees, 

 but be this as it may there are certainly cases of 

 tropical timbers where no such annual-rings, as they 

 are called, can be distinguished by the unaided eye, or 

 even with a lens : such timbers are said to be devoid 

 of " annual rings." I say " so-called annual rings," 

 because we are not yet sure that the periodic zones 

 correspond in all cases with annual increment, though 

 that is no doubt normally the case with all European 



