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VERTICAL AND LATERAL EXTENSIONS AND APPENDAGES 

 OF THE STEM 



Origin of Branches and Leaves. — Examining a radial section of the 

 tip of the stem (Fig. 4) we find, in addition to the structures already 

 considered as helonging ])rimarily to itself, protuberances, consisting 

 of masses of meristem tissue belonging to the periblem and the derma- 

 togen. Shortly, each of these tissue-masses assumes, in a general way, 

 the condition of the primary growing point of the main stem. Some 

 of them will develop into leaves, the structure of which will be con- 

 sidered farther on, others into branches, which latter j)r()cess is a mere 

 repetition of that already considered in relation to the })rimary stem. 

 In either case, the vascular bundles exhibit a connection, variable in its 

 details, with those of the stem from which it develops. 



Arrangement of the Leaves and Branches. — The normal method is for 

 a l)ranch and leaf to develop together, the former in the axil of the 

 latter, as already recorded. If two or more leaves, with their branches, 

 develop at the same node, it results in the opposite or verticillate 

 arrangement. If but one, then, of those developing at different levels, 

 each is successi\ely separated from the former by a uniform portion of 

 the stem circumference, so that a spiral arrangement results. This 

 s])iral will be considered when we come to the study of the leaf. 



Growth of the Internodes. The ])oiiit at which one or more leaves 

 de\elop has alread\' been defined as the node, and the poi'tion of stem 

 intervening between two nodes as the internode. At first tlu- internodes 

 are so short as to be scarcely perceptible, but they continue to grow 

 in all j)arts until a length more or less definite for the sjiecies is attained, 

 so that leaves and branches become separated by imiform vertical as 

 well as circumferential spaces. This brings us to another great distinc- 

 tion between tli(> stem and the root, in which latter we lia\-e found a 

 contiiuions and uniform longitudinal de\elopnient. 



Axils in which Buds do not Develop. The rule that a branch de\eloi)s 

 in each leaf-axil is habitually (lc|)arted from in the leaf-representatives 

 constituting the flower, and accidentally in sonic other cases. Its 

 failure to devel()|) may be tem]jorary, although oftiMi \-cr\ long con- 

 tinued, or it may be permanent. 



