CHAPTER XIV 



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 belonging primarily 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 process is a mere 

 repetition of that already considered in relation to the primary stem. 

 In either case, the xascular 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 branch 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 

 spiral will be considered when we come to the study of the leaf. 



Growth of the Intemodes. — The point at which one or more leaves 

 develop has already been defined as the node, and the portion of stem 

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

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

 in all parts until a length more or less definite for the species is attained, 

 so that lea\'es and branches become separated by uniform vertical as 

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

 tion between the stem and the root, in which latter we have found a 

 continuous and uniform longitudinal development. 



Axils in which Buds do not Develop. — The rule that a branch de\elops 

 in each leaf-axil is habitually departed from in the leaf-representatives 

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

 failure to de\'elop may be temporai-y, although often very long con- 

 tinued, or it may be permanent. 



