§ 22. ORGANIZATION OF VEGETABLES. 695 



simple group, the cellulares, called also the acotyledones, 

 from the absence of cotyledons, or seed-lobes, the tissue is 

 wholly cellular, the cells being nearly of equal size and con- 

 sistence ; mosses, lichens, sea-weeds, fungi, &c, are examples 

 (ante, p. 601). These plants have no flowers, and hence are 

 named cryptogamia. The vegetables belonging to the other 

 great class are termed vasculares, from their cellular tissue 

 being more complex, and assuming the structure of tubes 

 and vessels ; and phanerogamic, from their bearing flowers. 

 Their tissue is composed of cells of various sizes and forms, 

 and of straight and spiral tubes. This class is subdivided 

 into two families, viz. the monocotyledonous, so named from 

 the seed having but one fleshy lobe, or cotyledon (Lign. 154, 

 jig. 5), as the onion, lily, &c, and which are also called en- 

 dogenous, (from within), because increase takes place from 

 the innermost part of the stem ; and the dicotyledonous, 

 whose seeds have two lobes (fig* 4), as the bean, almond, 

 &c. ; these are likewise termed exogenous, from the new 

 matter being added externally to the old layers, and thus 

 forming annual circles of increase, as in the oak, elm, &c. 

 (fig* 8). A transverse section of the monocotyledonous 

 stems, (as the cane, palm, &c.) presents, therefore, openings 

 of tubes, which are condensed towards the outer surface 

 (fig- 7) ; while that of the dicotyledonous exhibits annular 

 lines of growth with diverging rays, and a central pith (fig* 8) ; 

 the latter character is of peculiar importance, because all the 

 other classes are destitute of a central cellular column. 



In some groups of dicotyledonous trees the elongated cells, 

 or tubes, are studded with ducts or glands (fig* 6), and this 

 is particularly the case in the woody fibres of the Conifera, 

 or cone-hearing trees ; so called from the fruit being in the 

 form of a cone, as in the pine, fir, &c. ; transverse sections 

 of the stems show the concentric layers and radiated struc- 



same character; and all the beautiful and apparently complicated 

 tissues of vegetables, are but modifications and expansions of these 

 simple elementary nuclei or vesicles. 



