24 



WRIGHT : THE GENUS DIO8PYRO8 



The dimensions of the vessels in the heart wood vary to a 

 slight extent ; in the first three or four years' wood the radial 

 diameter varies from O024 to 0*05 mm., the tangential dia- 

 meter from 0-024 to 0'06 mm., and the length from 0-20 

 to 0-35 mm. 



In the sapwood of the whole of our species the variation in 

 radial diameter is from 0*05 to 0'18 mm., and the variation in 



