GROSS ANATOMY OF "FLOWERING PLANTS, xiii 
old, it will probably shows everal more or less well-defined annual 
rings (Fig. 1). Notice that the rings are marked and defined by 
belts 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 piants 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. IJ), producing a spongy stem (as in some palms, In- 
dian corn, etc.), ora dense one (as in the canes, rattan, etc.). 
TL. In many herbaceous plants the wood 
is ina narrow ring, or ina 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 Hazogens (Figs. I and III), while 
those whose woody bundles are irregu- fie. III.—Cross-section 
larly placed, and which have no proper SR eehostr tnt nae: 
bark or pith, are known as Hndogens ing the bundles arranged 
' in a circle. 
(Fig. II). 
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 rootstock, common in many of the 
grasses and sedges as well as in numerous other plants. Some 
underground stems are much thickened, and are called tubers, as 
in 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 bulb the 
short stem (usually not much thickened) is covered with thick- 
ened scales, as in the onion. 
§ 2. Tur Roor., 
Form.—Most roots are cylindrical, or nearly so, in form, When 
of this form and quite small they are thread-like (filiform or fibrous). 
