THE STEM. 



21 



erect position, as is seen in the tufted habit of growth of plants with a 

 subterraneous main stem. (See also p. 15.) 



Buds. Every stem is developed from a bud, which consists of a 

 conical rudiment or growing-point of the stem bearing; rudimentary 

 leaves crowded upon its sides. The primary bud of the stem of 

 Flowering plants presents itself as the plumule (fig. 3) of the embryo ; 

 and so long as this axis continues to grow, a bud (the terminal bud) 

 is found at its extremity. The branching of a stem depends upon 

 the development of lateral buds, which, as a general rule, appear only 

 in the axil or upper angle between the base of a leaf and the stern, 

 whence they are called axillary buds. 



There is in many embryo plants a small portion of the axis intermediate 

 in structure as in position between the true root and the true stem (tig. 3). 

 This " hypocotyledonary axis " or tigellum sometimes gives off shoots, by 

 which it may be distinguished from roots ; moreover it is either cylindrical 

 or tapers upwards, while a root tapers in Y\f. 11. 



the opposite direction. This hypoco- 

 tyledonary axis forms the trunk of the 

 extraordinary plant called Welwitschia, 

 hereafter described. 



Nodes and Internodes. The 

 place whence a leaf arises marks 

 the position of a structural region 

 endowed with special physiological 

 activity; it defines externally a 

 point where the internal tissues have 

 a peculiar arrangement. Hence a 

 particular name is applied to it, that 

 of node. Sometimes a kind of arti- 

 culation of the stem occurs at this 

 point, but not as a general rule. 

 The intervals between the points of 

 origin of leaves are called the inter- 

 nodes. In buds, the internodes are 

 not yet developed. In a large 

 majority of ascending stems the 

 internodes become considerably de- 

 veloped, so that the leaves ulti- 

 mately appear stationed at distinct 

 intervals. In many subterranean 

 stems, at the lower part of the 

 stems of many herbaceous plants (fig. 11), and in the trunks of 

 many of the arborescent Monocotyledons, the internodes never 

 become much lengthened, and the leaves in consequence appear 



lantayo media bearing leaves 

 crowded on a stem with undeveloped 

 internodes. The short stem seen in 

 section. 



