LKSSON 25.] 



AND KXOr.KNOUS STKMS. 



151 



outer jiart of which is also (•.■Ihilar. This stnicliin* is very familiar 

 in foininon wood. It is really just the same in the stem of an herb, 

 only the wood is much less in quantity. Compare, for 

 instance, a cross-section of the stem of Flax (Fig. 352) 

 with that of a shoot of Maple or Ilorsechestnut of 

 the same ajre. In an herb, the wood at the bcfrinninj; 

 r-nnsist* nf .<;eparate ihreadr^ or little Wcu<>cs oi" woou ; 

 but these, however few and scattered tlu'y may be, ary 

 all so placed in the 

 stem as to mark out 

 a zone (or in the 

 cross-section a ring) 

 of wood, dividing the 

 pith within from the 

 bark without. 



420. The accompa- 

 nying figures (which 

 are diagrams rather 

 than exact delinea- 

 tions) may serve to 

 illustrate the anat- 

 omy of a woody 

 exogenous stem, of 

 one year old. The 

 parts are explained 

 in the references be- 

 low. In the centre is 

 thcPith. Surround- 

 ing this is the layer ..i;. 



of Wood, consisting both of wood-cells and of ducts or vessels. From 

 the pith to the bark on all sides run a set of narrow plates of cellular 

 tissue, called Medullary Rays : these make the silver-(/roin of wood. 

 On the cross-section they appear merely as narrow lines ; but in 

 •wood cut lengthwise parallel to them, their fixces show as glinimer- 



Flfi. 353. Cross-section of the stem of Flax, sliowing its liark, wood, and jiilli. 



Fit;. :t53. Piece of a stem of Soft Maple, of a year old, cut crosswise and lengthwise. 



FIG. :r>l. A |)orti(m of the same, magnified. 



Fit!. :t'>5. A small piece of the same, taken from one side, reaching from the hark to the 

 pith, and highly magnifli-d : n, a small hit of llio pilh ; h, spiral dnrls (if what is called tho 

 mrilitllwij sheath : c, the wood ; </, '/, dotted ducts in the wood ; c, f, annular ducts ; /, the liher 

 or inner hark ; it, the green hark ; A, the corky layer ; i, the skin, or epidermis ; /, one of the 

 medullary rays, or plates of silver-grain, seen on the cross-sectinn. 



