334 CONSERVATIVE OKGANS. [LECT. VII. 



course transversely through the wood ; and Mirbei 

 remarks that, " in many coniferous trees the di- 

 " vergent rays are not cellular ; but consist of ho- 

 " rizontal tubes which extend from the medulla or 

 " pith to the bark*." Whether they are cellular or 

 tubular, the layers, or masses, are flat, or in plates, 

 with the edges placed vertically, and thicker in 

 the centre than either above or below, appearing 

 therefore of a lozenge shape (see marginal plan, 

 p. 331) when vertically divided ; whilst in their 

 transverse section they display a slight inclination 

 to the wedge form -J-. They are much more deli- 

 cate in their structure than the concentric layers ; 

 and readily dissolve, like the common cellular 

 texture, so that when a thin tangental slice of 

 wood is macerated in water, the divergent layers 

 are decomposed and leave the meshes of the con- 

 centric layers empty, displaying the appearance 

 of a network or lace similar to that formed by 

 the macerated liber. 



From the cellular texture of the divergent lay- 

 ers, they are regarded by some authors as pro- 

 cesses of the pith or medulla ; and hence have 

 been named medullary rays ; and Mr. Keith ob- 

 serves, they are " apparently nothing more than 

 " the vesicles or cellular tissue of the pulp that 

 " originally existed in the alburnum now deprived 



* Elemens de Phys. veg. l re partie, p. 110. 

 t Vide Plate 6, fig. 2. g. 



