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 rapkides (from Rafn, the name of the discoverer,) are formed in the cells. 



'kJLA 



&m 



/ e d c b 



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

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

 fibre ; e, spiral vessel with a single fibre partly 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 their sides, the end of one tube ex- 

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

 It differs from cellular tissue, in the greater sti-ength, and, at the 

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

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

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



a. Tissue of this form constitutes the fibre of flax, hemp, &c., tlie 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 little glandular points, ar- 

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

 resinous wood, cliiefly 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 Coniferse. ^ 



32. Vasiform tissue consists of large tubes, called dotted 

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



