104 THE OAK 



I now proceed to some further details, which could 

 only be rendered intelligible in the light of the pre- 

 ceding preliminary remarks. 



After the cambium ring is once formed the daughter- 

 cells cut off on the inside of the cambium always 

 become transformed into one or more of the following 

 elements : 



(1) Some cambium cells which lie on the radial con- 

 tinuation of a medullary ray undergo a few horizontal 

 divisions across the long axis, and then simply pass 

 over as constituents of a medullary ray ; as the cam- 

 bium ring moves outwards, in consequence of the re- 

 peated formation of thickening rings, the periphery of 

 the cylinder of course increases, and this allows of more 

 space tangentially. One consequence of this is the 

 occasional and gradual widening of the medullary ray in 

 process of lengthening : this takes place to a small 

 extent only. Another consequence of the increased 

 space is the occasional interpolation of new medullary 

 rays. Eadial rows of cambial cells at points which lie 

 between the planes of two gradually diverging medul- 

 lary rays suddenly commence to form new medullary 

 rays. Hence, as the wood mass increases in radial 

 thickness, more and more of these interpolated medul- 

 lary rays appear, cutting up the wood proper into 

 partial sections. In succeeding years the cambium 

 keeps adding to the length of these rays, as it does to 

 that of the older rays, and again forms new ones between 

 as space increases. In the same ring about thirteen 



