88 COMPENDIUM OF GENERAL BOTANY. 



brief discussion of the characteristic activity of the cambium-ring 

 and the typical appearance of various sections of stems and roots. 



A cross-section shows the successive order of the products re- 

 sulting from the cambial activity, namely, the a,rrangement of the 

 wood-elements on one side of the cambium, and the secondary cortex 

 on the other side. Radial hands can be traced from the wood 

 through the cambium into the albumen-conducting tissue. It 

 should be noted that the primordial arrangement is, for various 

 reasons, very materially altered at some distance from the cambium 

 (lience at a later period). This secondary change consists mainly 

 in an increase in the size of the elements (gliding growth, Krabbe), 

 and in subsequent; divisions of the leptome-elements. As a rule, 

 the radial structure is most distinctly shown in conifers. The 





9 



Fig. 53. — Woody tissue of Taxus baccata (cross-section). 

 g. Limit of the year's growth; ni, medullary rays. (After Haberlandt.) 



cause for this can readily be explained. Elementary anatomy 

 teaches that vessels are wanting in the wood of conifers. Macro- 

 scopical examination of cross- sections shows this in the absence 

 of the large vascular lumina ; microscopically this is evident by the 

 large regularly arranged woody elements (tracheids and medullary 

 ravs). "Wood-parenchjTiia is rarely present. The following ele- 

 ments bring about a change in the anatomical appearance : 1 , resin- 

 ducts ; they usually extend longitudinally in the sparingly present 

 wood-parenchyma, or tliey may extend radially in the medullary 

 ray tissue ; 2, the difference between the growth-products in the 

 spring and in the aiitumn. 



The latter morphological factor (2) has a bearing upon conifer- 

 ous wood as well as upon dicotyledonous wood, and will receive 



