CHAPTER I. 



PROPERTIES, UTILIZATION, VALUATION, AND 

 DISPOSAL OF BARK AND ITS CONSTITUENTS. 



SECTION I. ANATOMY OF BARK. 



THE bark on a yearling shoot of dicotyledonous and gyiuno- 

 spermous woody species, at the close of the annual growth, may 

 be distinguished as outer and inner bark. The outer bark 

 (cortex) includes the external coating, termed epidermis, the 

 cells of which are covered by a suberous and ligneous, waxy 

 layer, the cuticle. Through the epidermis there are openings 

 (stomata), by which an interchange of gases is effected between 

 the interior of the plant and the atmosphere. The epidermis 

 contains frequently a strengthening tissue, the hypoderma, 

 formed sometimes of collenchymatous cells, the walls of which 

 swell when moist. Under the epidermis lie the chlorophyll 

 cells, connected together somewhat loosely, so that there is 

 room between them for the circulation of air. 



Usually in the first year of a shoot, the cells of the 

 epidermis or those of the subjacent cellular tissue, or even 

 of a deeper tissue, become divided ; the inner half form a cork 

 mother-tissue (Phellogen), whilst the outer half are brick- 

 shaped cork-cells. The latter lose their plasmic contents 

 rapidly and then contain only air, their walls become suberised 

 and are impermeable for air and water. Hence all tissues 

 outside the corky layer die. In order to replace the stomata, 

 a group of cells is formed beneath them, the walls of which 

 are rounded and suberised, so that the intercellular spaces 

 between them allow for the passage of air. These groups of 

 cells are named lenticels. In a few species, field-maple, 

 cork-elm, Phellodendron, and cork-oaks (Qucrcuis Saber, occi- 

 deutalis, coccifera, variabilis), etc., the cork thickens on the 

 stem and branches into ridges, or into continuous layers, when 



