22 



ELEMENTARY ORGANS. 



This occurs in the prickles of the rose, the stones of the plum, peach, &c., and in 

 the albumen of seeds. 



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

 called raphidcs (from the Gr. pa^pideg^ sewing needles,) are formed in the cells. 



o99999y 



FIG. 1. — Forms of tissue ; a, cutting of elder pith — cellular ; 6, cells from the gritty centre 

 of the pear; c, from tlie stone 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 time, the gi-eater tenuity, of its membrane. It seems de- 

 signed for the transmission of fluid, as well as for giving fiiiu- 

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



a. Tissue of this form 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 glandular points, ar- 

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

 resinous wood, chiefly of the fii" tribe (Conifercp,). 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. Witkam on fossil vegetables, ^c. 



32. Vasiform tissue consists of large tubes, called dotted 

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



