138 



VEGETABLE LIFE AND WORK. [SECTION 16. 



needle-shaped (rhapliides), as in stalks of Calla-Lily, Rhubarb, or Four- 

 o'clock, they are usually packed iu sheaf-like bundles. (Fig. 4G5, 460.) 



3. ANATOMY OF ROOTS AND STE.MS. 



423. This is so nearly the same that an account of the internal structure 

 of stems may serve for the root also. 



424. At the beginning, either iu the embryo or in an incipient shoot 

 from a bud, the whole stem is of tender cellular tissue or parenchyma. 

 But wood (consisting of wood-cells and ducts or vessels) begins to be 

 formed in the earliest growth ; and is from the first arranged in two ways, 

 making two general kinds of wood. The difference is obvious even iu 

 herbs, but is more conspicuous in the enduring stems of shrubs and 



trees. 



425. On one or the other of these two types the stems of all phanero- 

 gamous plants are constructed. In one, the wood is made up of separate 

 threads, scattered here and there throughout the whole diameter of the 

 stem. In the other, the wood is all collected to form a layer (in a slice 

 across the stem appearing as a ring) between a central cellular part vrhieh 

 has none in it, the Pith, and an outer cellular part, the Bark. 



4-J(). An Asparagus-shoot and a Corn-stalk for herbs, and a rattan for a 



woody kind, represent the first kind. To it 

 belong all plants with monocotyledonous em- 

 bryo (40). A Beau-stalk 

 and the stem of any com- 

 mon shrub or tree rep- 

 resent the second ; and 



. s.v: 

 '''i^* 



/-. _-^r 



to it belling all plants with dicotyledonous or polycotyledonous embryo. 

 The first has been called, not very properly, Endogenous, which moans in- 

 side-growing ; the second, properly enough, KroyefiOHS, or outside-growing. 

 427. Endogenous Stems, those of Monocotyls (10), attain their 

 greatest si/e and most characteristic development in Palms and Dragon- 

 trees, therefore chiefly in warm climates, although the Palmetto and some 



Fio. 471. Diagram of structure of Palm or Ynrra. 47-. Structure of a Corn- 

 stalk, in transverse and longitudinal section. 473. Santo of a small Palm-stt'in. 

 The dots on the cross sections represent cut ends of the woody bundles or threads. 



