154 VEGETABLE ORGANOGRAPHY. 



§ 3. — Of the "Woody Layers of the Wood and of the 



Alburnum. 



Between the central pith and the bark are found con- 

 centric layers or zones, which bear the name of the 

 Woody Layers (strata lignea, involucra lignea, 

 Malp. ; couches ligneuses). The assemblage of these 

 layers forms that which is commonly called the Wood 

 (hois) of the tree ; that which Malpighi calls the 

 Woody Portion (lignea portio J, and others the Woody 

 Body (corpus ligneum; corps ligneux), or Central Sys- 

 tem (systeme central). Grew designates it under the 

 name of the Main Body. This part, which forms the 

 solid base of trees, presents in old trunks two different 

 appearances; 1st. The central layers, which are harder, 

 more coloured, and evidently older than the external; 

 these form that which writers call the Heart-w-god; that 

 which naturalists designate under the name of W^ood 

 (lignum ; hois), or Perfect Wood (hois parfait) ; and 

 that which Dutrochet has recently proposed to call Du- 

 ramen. 2d. The external layers are more tender, of a 

 white colour, and evidently of a later date than the pre- 

 ceding ; they form the part which has received the name 

 of the Alburnum (alhurnum; a/iwrwa, Malp. ; auhier) 

 on account of its whiteness, or of the Imperfect Wood 

 (hois imparfait), because of its age, compared with the 

 Perfect Wood. 



In order to comprehend well the difference which is 

 found between the Wood and the Alburnum, it is neces- 

 sary to anticipate a little that which we shall hereafter 

 say upon the formation of the Woody Layers. Around 

 the Medullary Canal there is formed, during the first 

 year, a layer which immediately surrounds this canal ; 



