ghoss anatomy op floWebing plants, xiii 



old, it will probably shows everal more or less well-defined annual 

 rings (Fig. I). Notice that the rings are marked and defined by 

 oelts of ducts (pores) which constitute the " grain " of the wood. 

 In the centre is the pith, from which there extend towards or to 

 the bark narrow radiating lines — the medullary rays (rm). 



II. In some plants there is no distinction of wood and bark, as 

 In the canes. In such there are no annual rings, nor are there any 

 medullary rays. The ducts and their surrounding wood occur in 

 irregularly-scattered bundles which may be loosely or closely 

 pacKed (Fig. II), producing a spongy stem (as in some palms, In- 

 dian corn, etc.), or a dense one (as in the canes, rattan, etc.). 



III. In many herbaceous plants the wood 

 is in a narrow ring, or in a number of 

 separate woody bundles which are ar- 

 ranged more or less exactly in a circle 

 (Fig. III). In soft plants the bundles are 

 often very small and difficult to see. 



Plants whose wood is arranged in a cir- 

 cle, or which have annual rings, are 

 known as Exogens (Figs. I and III), while 

 those whose woody bundles are irregu- fio. iii.-cross- section 

 larly placed, and which have no proper fc'andytun (lbe"-isrshow- 

 bark or pith, are known as Endogens ing the bundles arranged 

 (Fig. II). in a circle. 



Underground Stems. — The student must not overlook the stems 

 which grow under the surface of the ground. They may gener- 

 ally be distinguished from roots by the scales or buds which they 

 bear. A common form is the rootstocTc, common in many of the 

 grasses and sedges as well as in numerous other plants. Some 

 underground stems are much thickened, and are called tulers, as 

 iij the potato, where the "eyes" are in reality the buds of the 

 thick stem. In the corm the short thickened stem stands vertically 

 and is coated with thin scales, as in Gladiolus. In the lulb the 

 short stem (usually not much thickened) is covered with thick- 

 ened scales, as in the onion. 



§ 3. The Root. 



Form. — Most roots are cylindrical, or nearly so, in form. When 

 of this form and quite small they are thread-like (filiform or fibrous). 



