SEED. 91 



100. The number of cotyledons varies in different plants, 

 which circumstance has given rise to the most important di- 

 visions of the vegetable tribes. There are also plants in wliich 

 this organ is wanting, and these constitute a distinct class, 

 called, 



Acotyledonoiis plants, which have no cotyledons in their 

 seeds : such plants belong to the class Cryptogamia, or flower- 

 less plants ; they have no embryo nor seeds, but • are repro- 

 duced from spores (minute grains resembling pollen) ; ferns 

 and mosses are of this class. 



Monocotijledonous plants have but one cotyledon, or lobe, in 

 the seed ; as the grasses^ liliaceous plants, palms, &c. They are 

 called Endogens on account of the peculiar growth of their stems. 



Dicotyledonous plants have two cotyledons ; they include 

 the greatest proportion of forest-trees, leguminous^ syngenesious 

 plants, &c. They are called Exogens. 



Polycotyledonoiis plants have more than two cotyledons, as 

 the pine and hemlock : such plants are not common. 



101. The Embryo first appears as a minute speck in the midst 

 of the pulp of the nucleus, near the foramen of the ovule ; it 

 gradually develops and assumes an organic state ; it lies in the 

 midst of the albumen, or at some of its extremities, or, when 

 there is no albumen, it fills the space within the integuments, 

 as in the Leguminous plants. As the embryo become's a plant 

 by the unfolding of its parts, it must contain within itself all 

 the essential organs. By laying open the seeds of many plants 

 the embryo becomes visible, as in the bean, orange, and apple. 

 The first part formed in the embryo is the axis^ its two ex- 

 tremities indicating the radicle and the stem ; the latter consists 

 of the node, furnished with the rudiments of a pair of leaves ; 

 tliese are the cot3dedons. That part of the axis which unites 

 the radicle and the cotyledon is called caulicle^ or tigelle^ from 

 the point where the cotyledons are united to the axis, a hud 

 is developed ; this bud contains the rudiments of the true or 

 primordial leaves, and is called the j)lumule, ov plitmida. It 

 may be seen lying between the cotyledons. "When the vital 

 principle is excited to action, vessels are formed and parts de- 

 veloped which were before invisible. The Radicle Fig. in. 

 unfolds itself into branches or fibers, which take 

 a downward direction, as if to avoid light and air, 

 from their peculiar structure, or from "their attrac- 

 tion toward the moisture of the soil. At Fig. 117, 

 appears the embryo in a germinating state ; a rep- 

 resents the radicle^ I tliQ j)lu?mde^ c the fanicle, by 

 means of which the plant is still connected to the cotyledons ; 



100. Division of plants as respects cotyledons.— 101. First appearance of the embryo— Part first 

 fonned— The node— Plume— Radicle. 



