ANATOMY OF WOOD. 9 



other nutritive materials. Whilst the pith is important in the 

 growth of yearling shoots, later on, irrespective of its dia- 

 gnostic value it is unimportant as a factor in the quality of 

 most woody species. Only, as in palms, in species the annual 

 shoots of which do not increase in thickness, is the pith of any 

 moment in the quality of the wood. 



Around the pith are some of the longest organs, vessels 

 (trachea) and tracheids. The widening of the cells of the 



-I li 



u a b 



l-'i-. l. Transverse section of beechwood. Magnified inn in 

 <i N:irrn\v pith-ray, h I'.road pith-ray. / I'-oimdary of an annual 

 rin,L, r . The lar^e pores are transverse sectiona of vessels. The 1 hick- 

 walled elements with narrow lamina are wood-fibres ; t ho>c with 

 thinner walls and wider lamina, wood-parenchyma or tracheids. 

 K. llurtijr. 



meristem, or primary growing tissue of the yearling shoot 

 (perhaps also their lengthening), is caused hy the water taken 

 from the plasmic contents of the nascent organs. Whenever 

 vascular cells stand OIK; above the other, the separating trans- 

 verse walls of a number of them are absorbed so as to form 

 vessels. Various kinds of thickening then line their lumina, 

 and they are termed spiral, annular, or scalariform vessels. As 

 soon as the vessel has attained its normal width, during the 

 year of its formation, its plasniic contents and the water 

 contained in its lumina disappear. Mayr's observations are 



