16 WOODY TISSUE. 



23. Under tliis form of tissue is usually arranged a variety- 

 found mostly in the roots of plants, and which appear to be 

 spiral vessels with the fiber broken into short pieces and at- 

 tached to the tube. This is called continuous bothrenchyma, 

 differing from the one above described in having no interrup- 

 tions caused by the adherence of the cells. 



Woody Tissue. 



24. The woody tissue consists of elongated vessels tapering 

 at each end to a very fine point, which become thickened by 

 the deposition of sclerogen till the cavity is nearly filled, and 

 the fiber becomes hard, elastic, and unyielding. 



It is the fine shining fibers which are readily distinguished 

 in wood, and which are composed of many woody fibers, formed 

 into bundles. So minute are the individual fibers, that the 

 finest filament of flax, which is composed of woody fiber, is made 

 up of a great number of these fibers joined together ; their fine 

 tapering extremities being spliced to like fibers, which go to 

 make up the long fiber extending through the whole plant. 

 Cotton is of the common cellular formation. A modification 

 of the woody fiber occurs in the coniferous plants ; the indi- 

 vidual fibers are larger in this family, and are marked 

 by depressions which appear like disks. These de- " 

 pressions on one fiber are always opposed by a similar 

 depression in the neighboring fiber, like two watch- 

 glasses placed edge to edge, as seen in Fig. 15, and 

 these may be easily seen in the thin longitudinal slice jj 

 of the pine placed in water and viewed through a 

 microscope. |^ 



25* It is this form of tissue that gives strength to || 

 vegetables. Without it the stems of trees would be 

 unable to bear their own weight, much less could they 

 be used, as they now are, as materials of strength. The sinRie'sber 

 branches of the oak or hickory, destitute of the woody onhePiS 

 fiber, would break as easily as a mushroom. Besides 

 forming a part of the wood, it is found in the bark and midrib 

 of leaves. It protects other and more delicate portions, and 

 gives form to the plant, appearing to occupy the same place 

 in the vegetable economy that bones do in the animal. In its 



24. Of -what does the woody tissue consist ? How does it become thick- 

 ened? Where seen? What does it make up? What peculiar in Co- 

 niferge ?— 25. What gives strength to vegetables ? "Where found besides in 

 the wood ? 



