22 



ELEMENTARY ORGANS. 



This occurs in the prickles of the rose, the stoues of tlie plum, peach, &e., and in 

 the albumen of seeds. 



/. In some plants, as in the Turkey rhubarb, &c., little bundles of crystals 

 called raphides (from the Gr. pa<pide^, sewing needles,) are formed in the cells. 



FIG. 1. — Forms of tissue ; a, cuUmg of elder pith — cellular; t, cells from the gritty centre 

 of the pear; c, from the slone of the plum — both strengthened by solid matter; rf, woody 

 fibre ; e, spiral vessel with a single fibre panly drawn out ; /, vessel with a quadruple fibre. 



30. Woody tissue, called also fibre, consists of slender, 

 transparent, membranous tubes, tapering to a point each way, 

 and adhering together by then sides, the end of one tube ex- 

 tending beyond that of another, so as to form continuous threads. 

 It differs from cellular tissue, in the greater strength, and, at the 

 same tune, the greater tenuity, of its membrane. It seems de- 

 signed for the transmission of fluid, as weU as for giving firm- 

 ness to those parts which need support. (Fig. 1, d.) 



a. Tissue of this foiin constitutes the fibre of flax, hemp, &c., the ligneous sub- 

 stance of the stems and roots, the petioles, and veins of leaves, &c. 



31. The most remarkable modification of the woody fibre, is 

 that called glandular. It consists of httle gltmdular points, ar- 

 ranged along the walls of the woody tubes. It occurs only in 

 resinous wood, chiefly of the fir tribe (Coniferce). It has fre- 

 quently been detected by the microscope, in fragments of fossil 

 coal, whence it is inferred that coal-beds originated from buried 

 forests of the Coniferas. Witham on fossil vegetables, 4*c. 



32. Vasiform tissue consists of large tubes, called dotted 

 ducts, having numerous little pits, sunk in the thickness of its 



