144 



THE LIGNEOUS SYSTEM. 



600, Section of an ^crogenons stem of Tree- 

 Fern (Cyathea), showing the vascular bundles 

 imbedded near the circumference of the cel- 

 lular mass. 



722. ThaI;L06ens are the lowest 



in the scale of rank, having no true axis 

 699, Various kinds of vessels in a wood- ^^^ ^^ ^^^^^ ^^^^^^ ^^^^ parenchyma, 

 aber of Bamboo or Eattan. a, Cells of paren- '^ . •" . ' 



ehyma; 6, annular cells; e, 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, puff- 

 balls, frog-spittle, mildew). 



723. The stetjotube of boots presents few deviations from that of the sterna 

 to which they severally belong, being exogenous hi Exogens, 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. 



601 602 724. The FiBRiLLiE 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 mouths of the 

 growing plant. 



725. The pileorhiza. The mi- 

 croscope shows that the extreiftie, 

 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 (pOeus, 

 flbrlllffl and (s) pileorhiza. 602, Two plants of a cap, rhiza, root), which consists of 

 Lemna minor (Duckmeat). e. Their pileorhiza. ^i^er, hardened cells, behind which 

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

 sheath. 



72G. The mannbb op geowth in the boot is not like that of stems, by the 

 extension of parts already formed, but simply by the addition of new matter at the 



