144 



THE LIGNEOUS SYSTEM. 



MO 



600, Section of an Aorogonous stem of Tree- 

 Fern (Cyathea), showing the vascular bundles 

 imbedded near the circumference of tho cel- 

 lular mass. 



722. Thailogens are the lowest 

 in the scale of rank, having no true axis 

 599, Various kinds of vessels in a wood- ^^^ ^^ ^^^^^ y^g^^ ^^^^^ parenchyma, 

 fiber of Bamboo or Eattan. a. Cells of paren- ■ ^u j • ■ 



chyma; i, annular cells ; c, spiral vessels ; which grows m threads or in mass in 

 d, porous duct ;«, wood-cells. all directions. The apparent stems 



(stipes), if any, support the fructification only (sea-weeds, lichens, mushrooms, puif- 

 balls, frog-spittle, mildew). 



723. The stktjotuee of koots presents few deviations from that of the stems 

 to which they severally belong, being exogenous in Bxogens, endogenous in En- 

 dogens, etc. In the former class the central pith disappears, its place being occu- 

 pied mainly by vascular ducts, and the liber, if any, has no bast-cells. 



724. The fibrilljb and pileor- 

 hiza should, however, be mentioned 

 as peculiar in the structure of the 

 root The former are produced by 

 millions, clothing the delicate epi- 

 dermis of the young rootlets as with 

 cottony down, especially in light 

 soils. They usually consist of a 

 single cell of the epidermis extended 

 as seen in figure 601. They are the 

 true absorbents, the mMdhs of the 

 growing plant. 



725. The pileokHiza. The mi- 

 croscope shows that the extreme, 

 advancing point of the delicate, grow- 

 ing fibers is not thrust naked against 

 the opposing soil, but iS covered 



601, Extremity of the rootlet of Maple, with "with a cap called pileorhiza (pikus, 

 flhrillae and («) ptteorhiea. 602, Two plants of a cap, rhiza, root), which consists of 

 Lemna minor (Duckmeat). «, Their piUorhissa. oi^gr, hardened cells, behind which 

 are formed the new cells. In the Duck-meat the pUeorhiza is lengthened into a 

 sheath. 



726. The manner op growth in the root is not like that of stems, by the 

 extension of parts ^Ir^eady formed, but simply by the addition of new matter at the 



