254 



INDUSTRIAL PLANTS 



connected as to form a sort 

 extend radially the plates of pitl 



Fic. 'J'.i'S. — Diagram of niaple stem 

 showing the development of wood 

 and bark through first and second 

 years. At the tip is a mass of 

 living formative material (shown 

 unshaded) from the sides of which 

 arise protrusions that finally In- 

 come leaves. Also arising from the 

 formative region, just above the 

 base of the very young leaves, are 

 protrusions which develop into 

 formative regions like that of the 

 main tip, and, as growing-points, 

 produce leaf-bearing branches of 

 the main stem. In the center, 

 around the axis, the formative n:ia- 

 terial as it grows older becomes 7^'i^h. 

 (shown as dotted), and this pith is 

 continuous with that of the 

 branches. The surface becomes 

 changed into a skin or epidermis 

 (shown by coarse shading), cover- 

 ing both stem and leaves. Parts 

 of the formative material between 

 the epidermis and the pith become 

 variously hardened into bundles of 

 fibrous materia! : around the central 

 pith arise strands of wood (shown 

 by fine shading) ; near the epidermis 

 arise corresponding strands of bark 

 (shown by black), surrounded by 

 more or less pith-like material 

 which may become green, corky, 

 or otherwise peculiar (shown dotted 

 like the pith) ; and between the 

 rings of wood and bark is a layer 

 of formative material which is con- 

 tinuous with that of the tip and* is 

 called the cambium. From this 

 cambium in successive years new 

 W'ood is added to that within and 

 new bark to that on its outer side, 

 and thus both wood and bark in- 

 crease in thickness by annual lay- 

 ers. But on the outside the epi- 

 dermis, and then the older bark, is 

 pushed off or worn away so that 

 the total thickness of the bark is 

 limited. Both wood and bark are 

 continued into the leaves, but not 

 the cambium. The strands of 

 wood and those of bark are so 

 )f network through the meshes of which 

 called jtith-rays. (Original.) 



a layer of canihium Ix'twoen. These strands eonnect with 

 similar ones in the leaves, and are continuous below with the 

 ring; of strands forniiiii*; between the wood and the bark 

 whieh A\-as J"ully fuj'nied ^\ lien the season b(^gan (Fig. 233). 



