THE STEM 29 



THE STEM 



The stem is the axis of the plant which bears leaves, flowers, and 

 fruit so that each shall be in the most favourable position for 

 performing its functions. The leaves are separated from each other 

 by greater or less distances called internodes. Sometimes these inter- 

 nodes are so short that the plant appears to be stemless or almost 

 so, as in the Primrose and Houseleek. Stems always originate in a bud, 

 the first one arising between the seed-leaves from the small bud known 

 as the plumule. Branches arise also from buds in the axils of leaves, 

 and this gives the spreading habit so characteristic of trees and shrubs, 

 all belonging to the Dicotyledonous and Gymnospermous groups of 

 plants (see p. 122). Among the Monocotyledons (p. 127) and Ferns 

 (p. 1008) buds at the end of the stem only are developed, hence the 

 usually unbranched character of their stems. 



In the lower orders of plants, such as Seaweeds, Liverworts, 

 Mushrooms &c., stems are unknown. The first trace of a stem 

 appears in the Mosses, and becomes more marked in the Clubmosses 

 (p. 1024), Horsetails (p. 1023), and Ferns (p. 1008) ; but the stem as 

 generally understood attains its greatest development in the plants 

 belonging to the flowering groups, as seen in the Oak, Apple, Beech, 

 Elm, Pine &c. Whether they are herbaceous, that is, soft, tender, and 

 deciduous as in annuals and biennials (p. 78), and herbaceous 

 perennials (p. 86), or woody as in trees and shrubs (p. 107), the stems 

 of all flowering plants have their origin in the ' plumule ' or first bud 

 of the embryo plant. 



STEUCTUEE OF STEMS 



Besides the differences in stems referred to below, it may be 

 mentioned here that there is a very marked difference in the structure 

 of the stems of Dicotyledonous plants (p. 122) and those of Monoco- 

 tyledons (p. 127). An examination of the stem of a Willow, Apple, 

 Fuchsia, Wallflower, or any other plant belonging to the Dicotyledonous 

 group will show in transverse section that it consists of three distinct 

 parts, viz. (i.) the pith in the centre; (ii.) then the wood; and (iii.) 

 the bark or rind outside. The bark is readily peeled off, especially 

 when the sap is flowing upwards in spring, and it leaves the white 

 wood exposed to view. On the outside of the wood and next the bark 

 is a very important layer of quick-growing and actively dividing cells 



