26 GENERAL PRINCIPLES. 



r 



dermis, gives to the young growth of trees its peculiar 

 color, by means of which the experienced cultivator is 

 enabled to distinguish varieties, even when not in leaf. 

 Within the corky layer is 



3. The Green Layer (E), which gives to the young 

 shoots their green color. This, as the wood ripens, is 

 soon covered by the corky layer. 



The Inner Bark, or Liber (F). This is the interior 

 portion of the bark, in immediate contact with the wood. 

 It is composed of perpendicular layers of soft, flexible 

 but very tough fibres. It is this part of the bark of the 

 Bass\vood that is used for tying in budding, etc., the tissue 

 being separated by maceration. 



The bark remains with these distinct layers, only for .1 

 few years. It scales off, and falls away in forms varying 

 with the kind of tree, but in all cases a portion of the in- 

 ner bark is left attached to the tree. In the grape-vine, 

 the inner bark, or -liber, is renewed each year, and that 

 formed the year before is thrown off in long shreds. 



Within the bark we have the Avood, and in the center 

 the pith. The wood is divided into 



1. The Sap-wood (included in the dotted line ). This 

 is the youngest, or last formed, layer of wood, immediate- 

 ly below the inner bark. It is distinguished in all trees 

 by being softer and lighter colored than the older parts. 



2. The "Heart, or Perfect wood. This is the central, 

 or interior portion of the stem, or branch, grown firm and 

 mature by age. It is generally a shade darker in color 

 than the newly formed part, or sap-wood. As the en- 

 graving, fig. 2, shows a stem only one year old, this is 

 not represented. 



3. The Pith (6r). This is the soft, spongy substance 

 in the center of the stem nnd branches. In soft-wooded 

 species, like the grape-vine, it is large ; in hard-wooded 

 species, as the apple, pear, quince, etc., it is small. In young 

 shoots it is soft, green, and succulent, and fills an impor* 



