GE0S8 ANATOMY OF THE ANGI08PBRM8. 293 



The Bark. — Witli a sharp knife dissect the bark of a twig, notic- 

 ing — 1st. The thin outer part, the epidermis. 2d. A soft layer 

 beneath it, the soft hark (which is entirely green, or partly green and 

 partly colored, or more or less corky). 3d. A layer oi fibrous iark, 

 often called hast. Dissect the bark of older parts of the stem and 

 notice the disappearance of the epidermis and the soft bark. The 

 fibrous bark has here become intermingled with more or less corky 

 matter, and has been ruptured into scales, ridges, and furrows. 



The Wood. — I. With a sharp knife cut across the stem and examine 

 the portion inside of the bark. If of a stem several years old, it will 

 probably show several more or less well-defined annual rings (Fig. 

 178). Notice that the rings are marked, and defined by belts of duets 

 (pores) which constitute the ' ' grain "of the wood. In the centre is 

 the pith, from which there extend toward 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 

 scattered independent bundles which may be loosely or closely packed 

 (Fig. 179), producing a spongy stem (as in some palms, Indian corn, 

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



III. In many herbaceous plants the wood 

 is in a narrow ring, oi' in a number of sep- 

 arate woody bundles which are arranged 

 more or less exactly in a circle (Fig. 180). 

 In soft plants the bundles are often very 

 small and difficult to see. 



Plants whose wood is arranged in a 

 circle, or which have annual rings, usually 

 have two cotyledons in their embryos, and 

 are known as Dicotyledons (Figs. 178 and 

 180), while those whose woody bundles are fkj. 180.— Cross-section 



independent and scattered and which have °| ^^^^ herbaceous stem 

 ^ , , .,, ,, , , , of a Candytuft (Iberis), 



no proper bark or pith, usually have but showing the bundles ar- 

 one cotyledon, and are known as Monocoty- ranged m a circle, 

 ledons (Fig. 179). 



Underground Stents. — The student must not overlook the stems 

 which grow under the surface of the ground. They may generally 

 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 



