42 



ANALYTICAL CLASS-BOOK OF BOTANY. 



a subterranean brancli, which, becoming greatly thick- 

 ened, developes into a fleshy knob, having numerous buds. 

 The Potato, in which the buds have the popular name of 

 eyes, is a familiar instance. The Jerusalem Artichoke, 

 fig. 2, Plate X., is also a fine example. The tubers, 

 in different stages of progress, are seen crowning the 

 several branches ; while one of them, exhausted by the 

 efforts of the preceding year, has no buds. The Tuber is 

 well stored with starch, to be expended in the future 

 growth of the plant. 



241. The Bulb may be defined as a subterranean 

 Bud, usually clothed with scales, which, like those of the 

 Bud, appear to be undeveloped leaves, as in the Lily, fig. 

 5. If the bulb consists of concentric layers, it is said to 

 be tunicated, or coated, as in the Onion. A transverse 

 section of this kind of bulb, showing the layers, is seen 

 at fig. 7. The vertical section of a Bud, fig. 6, and that 

 of the Lily-Bulb, fig. 9, illustrate the analogy of structure 

 between the Bud and Bulb. The latter is, to all intents 

 and purposes, a subterranean bud. 



242. BuLBLETs are small aerial bulbs, which are de- 

 veloped in the axils of the leaves, as in the Tiger-Lily, fig. 8. 



243. The Coem is a solid bulb of a round form, and 

 a compact, uniform texture, as in the Wake-Kobin, and 

 the Meadow Safixon, an English plant, fig. 3. At a is 

 the old corm, nearly exhausted, while the fresh new corm 

 is seen at h. 



244. The Rhizoma is a thickened horfzontal stem. 

 It has the same mode of growth as the aerial forms, in- 

 creasing at the apex from a terminal bud. The scars of 

 former stems are to be seen on its surface, and to these 

 marks- the Solomon's Seal, fig. 4, is indebted for its name. 

 The Sweet Flag, Ginger, and our native Iris, are also 

 examples. 



245. The Creeper is a variety of Rhizoma, from 

 which it differs chiefly in size. The Garex arenaria, 

 fig. 1, is a creeping stem, which often renders important 

 service in binding the loose sands of low maritime shores. 

 The terminal bud, in this plant, remains subterranean 

 during the first year. In the second year it ascends, 

 puts forth a creeping branch, with a cluster of leaves and 

 roots ; and year after year this operation is repeated, the 

 plant thus extending itself indefinitely. At 3 is the stem 

 of the present year, at 4 a section of the last year's stem. 

 The Knot-G-rass, a troublesome weed in door-yards and 

 gardens, has a very branching stem of this kind. It is 

 so extremely tenacious of life, that if but a single joint 



What 18 deposited in the Tuber, and for wliat purpose f How is the Bulb 

 in the Lily ? How in the Onion ? Most obvious functions of the Stem ? What 

 other functions f What office has it between the Eoot and Leaves ? Describe 

 the ascent of the Sap. By what law does it rise— through what parts, in the 



is left it will grow and spread rapidly, so that, if it once 

 gets rooted, it is very difiicult to exterminate. 



FUNCTIONS OF THE STEM. 



246. The most obvious design in the structure of the 

 Stem consists in the mechanical support which it affords 

 to the superincumbent growth, but it has also equally 

 important vital functions. The Stem keeps up a more 

 or less active communication between the remotest vege- 

 table organs, the Root and Leaf; and thus it is mani- 

 festly a great conducting medium. The Root absorbs 

 the surrounding liquids and gases by endosmose. These 

 constitute the Crude Sap, which, with every step, as it 

 rises, meeting with denser, because more highly elabo- 

 rated liquids, it continues to ascend by the same law, 

 under the influence of the superior vital law, finding 

 passage in the early stages of growth mostly through the 

 dotted ducts, but afterwards through the newer wood. 

 When arrived at the branches, the currents are subdivided 

 and sent into the branchlets ; thence, by innumerable 

 ramifications, they pass into the leaf-stalks and veins, 

 whence they again repeatedly diverge ; and thus enter- 

 ing the smaller veins and veinlets, they visit and refresh 

 the remotest particles of the leaf. There, having been 

 acted upon by the light, in a manner hereafter to be 

 more particularly described, the innutritions portions re- 

 jected, and the nutritious elements more highly elabo- 

 rated, they form a whitish, and somewhat viscid sub- 

 stance, which is known as Cambium, or Elaborated 

 Sap. 



247. The liquid thus prepared holds in solution the 

 Elements of the Vegetable Tissues; and having com- 

 pleted its tour in the leaves, it immediately sets off on 

 its homeward journey to the Root ; but only a small por- 

 tion eventually arrives there. On its passage through 

 the Stem, it deposits the Cambium Layer (202) ; and 

 from this stratum is sent forth nutriment, which, taken 

 up by the Medullary Rays (198), passes into the Albur- 

 num (201), and all the vital parts of the wood. Thus a 

 new layer of wood is formed on the one hand, and of bark 

 on the other. 



248. Nor is this all. A considerable proportion of 

 the Cambium is appropriated to supply those cells in 

 which the peculiar products of the plant are elaborated. 

 These are found mostly in the Bark, which is generally 

 the chief place of deposit for the medicinal and other 

 active properties of the plant. Continuing these offices 



young state — afterward — what higher law — what changes— how docs it progress 

 — how diverge — what at last reach — what change — by what influence — what 

 separation occurs — what is it then — what hold in solution? Describe the pas- 

 sage back. Through what strata does it pass ? What deposit? 



