20 



ANALYTICAL CLASS-BOOK OF BOTANY. 



in nothing is this inherent love of beauty more truly de- 

 veloped than in the study of Flowers. 



CHAPTER X. 



ORGANS OF VEGETATION. 



112. With the first influence of life, the young plant 

 is acted upon in two opposite directions. A certain point 

 takes a downward course, fixes itself in the earth, and 

 becomes a Root. This is the Descending Axis. The 

 opposite point, being as strongly determined upward, 

 rises into the air, and produces a Stem and Leaves. 

 This is the Ascending Axis, sometimes also called the 

 Axis of Growth. These three, the Root, Stem and 

 Leaf, are called Organs of Vegetation. They con- 

 tain all that is essential to the nutriment and growth of 

 plants, and all other organs are but repetitions or trans- 

 formations of these. Each has its peculiar office in the 

 vital economy, and yet they are so nearly related, that in 

 certain cases the functions of one may be supplied by 

 another. 



113. Having taken a brief view of the elements of 

 organism in the Plant, let us proceed to the History, 

 which you will now be much better able to understand. 

 The earliest knowledge we can have of a plant, individ- 

 ually considered, or as constituting a single whole, an 

 entire being, is that of an Embryo contained in the seed, 

 and here should its biogrsiphy begin. 



114. The Vegetable Embryo is of various forms, 

 the most common being that of a club-shaped body, 

 gashed or lobed at one end, as in fig. 4, Plate V. It 

 consists of three parts — the Radicle, the Plumule and 

 the Cotyledons. 



115. The Radicle is the undivided end of the em- 

 bryo, and is seen at h, fig. 4. This is the primary axis, 

 from which are developed all other parts of the plant. 

 It is the rudimental stem from which both Root and 

 Stem proceed. 



116. The Plumule is the young bud which crowns 

 the radicle, and is inclosed within the cotyledons. It 

 contains the rudiments of the axis of growth, which, in 

 the process of time, developes stem and leaves, with all 

 their subdivisions, varieties and transformations. 



117. The Cotyledons. — The upper portion of the 

 embryo usually consists of two foliaceous and fleshy 

 organs, called the Seed Leaves, or Cotyledons. They 



General eubject First influence of life. What is the Root sometimes 

 called? Stem. Organs of vegetation, what contain ? Earliest knowledge of a 

 plant Parts of the embryo. Eadiclc, what does it develope ? Plumule. 

 Cotyledons, character and otfice. What sometimes called? How many usu- 



enfold the young bud before expansion, and generall} 

 rise above the surface, appearing as a pair of greatly 

 thickened leaves, which are conspicuous in the Garden 

 Bean, as at c c, fig. 7. 



118. If a seed of the Garden Bean or Pea be soaked 

 in water for a day or two, it will spontaneously or easily 

 separate in two parts, which are the cotyledons, for in 

 such fleshy seeds the seed-leaves constitute almost the 

 entire bulk. Between the cotyledons will be seen the 

 young plant, with its first pair, or Primordial Leaves, 

 nicely folded, and conspicuous even before germination. 

 At fig. 9 is a seed of the Garden Pea treated in this 

 way. The cotyledons, c c, constitute almost the entire 

 seed, being invested only with a skin. Between them 

 the embryo is very distinct, with its young bud, or 

 plumule, J), its radicle r, the common axis t, and the 

 cavity on one side at h, where the plumule had b^-en de- 

 posited. But if an oat, rye or wheat grain be subjected 

 to the same process, no separation occurs, because there 

 is but one cotyledon. 



119. The First Subdivision. — Taking the above 

 facts into consideration, Phssnogamous plants are sepa- 

 rated into two great ranks, according to the number of 

 their seed-leaves. Those which have two are termed 

 Dicotyledones, or Dicotyledonous plants; and those 

 which have but one, Monocotyledones, or Monocoty- 

 ledonous plants. The Dicotyledones include most of our 

 forest trees, shrubs and herbaceous plants, and they are 

 represented in the plate by the beautiful Almond tree, 

 fig. 2, the Garden Bean in various figures, the Moth 

 Mullein, fig. 10, the delicate little Bell flower, flg. 17, and 

 the Shrub, fig. 13. The Monocotyledones, which enibrace 

 the Palm, Grass and Lily tribes, are seen in the White 

 Lily and Blaize, figs. 1 and 6, in the Oat-grain, fig. 11, 

 and in various figures of the last plate. In their mode 

 of growth, their whole structure, and all their habits, 

 these two great divisions present the most remarkable 

 differences, which will be defined in a consideration of the 

 Stem. At fig. 6 is a grain of Maize germinating : t is 

 the radicle, c the cotyledon, and g the plumule, unfold- 

 ing the primordial leaf, which, as all who have observed 

 such plants know, rises above the earth like a little blade 

 of grass. In Monocotyledones, the cotyledon never ap- 

 pears above ground ; while in Dicotyledones, the seed-leaves 

 rise into the air, or, in the common phrase, they " come 

 ttp." The Oak, and a few other plants, are exceptions, 

 their seed-leaves never rising above the ground. 



ally? In om" common forest trees and herbs how many ? In the Palm, Gmss 

 and Lily tribes ? First gi-eat subdivision of plants, on what founded? What 

 plants usually send up their cotyledons in germination ? What exceptions 1 

 What do not? Plants with two cotyledons. Called what? With one ? 



