144 



THE LIGNEOUS SYSTEM. 



too 



600, Section of an Acrogenous stem of Tree- 

 Fern (Cyathea), showing the vascular bundles 

 imbedded near the circumference of the cel- 

 lular mass. 



722. Thallogens are the lowest 



in the scale of rank, having no true axis 

 599, Various kinds of vessels in a wood- &nd nQ Qther tLsgue thaQ pareuchvma 



fiber of Bamboo or Rattan, a, Cells of paren- r . • 



, . - , „. . . c „:,.„i „„„„!, . which grows m threads or in mass in 



cbyifti; 0, annular cells; c, spual vessels, e 



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



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

 balls, frog-spittle, mildew). 



123. The structure op roots presents few deviations from that of the stems 

 to which they severally belong, being exogenous in 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. 



724. The fibrill^: 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 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 (pileus, 

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

 Lomna minor (Duckmeat). «, Their pileorhiza. ider, hardened cells, behind which 

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

 aheath. 



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

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



