358 



THE ANATOMY OF WOODY PLANTS 



of the pith. Not only is the structure of the wood in the genus 

 under discussion contrasted in the nature of its radial parenchyma 

 with that of the Coniferales, but it also presents a striking resem- 

 blance to the dicotyledons in the possession of true vessels, albeit 

 of a primitive type. The correlation of large rays and true vessels 

 in the organization of the wood in both Gnetales and dicotyledons 

 is a feature which is clearly not without evolutionary significance, 

 as will be shown in subsequent pages. The pith is of moderate 



size and the phloem 

 and cortex constitute 

 a rather thin layer 

 on the surface of the 

 strongly convoluted 

 woody cylinder. The 

 depressions on the 

 face of the wood 

 plainly correspond to 

 the position of the 

 large rays, as is the 

 case with identical 

 conditions in certain 

 dicotyledons. 



In Fig. 256 is 



FIG. 25 5.-Transverse section of the stem of shown a transverse 

 Ephedra gerardiana. View of the Structure 



of the wood some- 

 what highly magnified. The features presented by the vessels 

 and rays stand out very clearly. It is obvious that annual rings 

 are present, although not conspicuously developed. The paren- 

 chyma is of diffuse distribution as in the higher conifers. The 

 large rays, however, illustrate interesting and phylogenetically 

 important features. Even in the transverse view they are clearly 

 composite structures and do not consist homogeneously of paren- 

 chyma, as in the corresponding radial bands in our northern 

 oaks and in the genus Gnetum. Vessels are seen intimately 

 incorporated in the organization of the ray. The vascular are 

 not the only elements of the longitudinal structure of the wood 



