154 EXTENSIONS AND APPENDAGES OF THE STEM 



Occasional Failure of the Leaf to Develop. — Upon the other hand, the 

 subtending leaf niay fail, accidentally, or in a few cases habitually, to 

 develop, so that the branch does not show its axillary nature. 



Abnormal Position of Branches. — Finally, we note that a branch may 

 accidentally, or in some cases habitually, develop from some other 

 point than the leaf-axil, or two or more may develop, at least partially, 

 from one axil, either side by side or in a vertical row. 



Not only may a lateral branch thus fail to develop, but the apical 

 extension of the growing point may fail, accidentally or habitually, 

 the growth being continued by means of one or more branches only. 



Sympodial and Monopodia! Stems. — When this method of growth is 

 characteristic, the new branch taking the place of the suppressed stem 

 which produced it, at each successive node, so that the stem becomes 

 composed of a succession of one-jointed branches, the stem is called 

 Sympodial, as contrasted with the term Monopodial, for the ordinary 

 form, in which the apical growth, as well as that of the branches, is 

 continued from joint to joint. 



The natural result of such a series of branchings would be to produce 

 an angular divergence of the axis at each joint, as the branch projects 

 more or less laterally from its support. This, however, is usually not 

 the case. In many plants the new branch takes the erect position of 

 that which it has replaced, preserving the rectitude of the axis, and so 

 tending to obscure the sympodial nature of its growth. In such cases, 

 we must search for other indications of its nature. This subject will be 

 understood upon reference to the accompanying diagrams (Figs. 428 

 to 430), in which a in each case represents the apical extension, b the 

 leaf, c the axillary branch. It is seen that the positions of the three, 

 with relation to each other, are the same in e^'ery case, the axillary 

 branch being between the other two, no matter what changes in their 

 directions may occur. In Fig. 429 the apical ph^-tomer has been 

 forced a little to one side, while in Fig. 430 it has become perfectly 

 horizontal, the branch substituting it in the erect position. It is clear 

 that in the last case, c might easily be mistaken for the main stem, 

 a for a branch. If this view is taken, however, we are at once met by 

 the difficulty that the supposed branch has no leaf at its base, that is, 

 it is not axillary, while the leaf, b, has no branch in its axil. Both these 

 difficulties entirely disappear when we regard the body between the 

 other two as the branch. 



A mistake becomes even more easy when one of the structures 

 becomes modified into some unusual form. Thus, in Fig. 431, the 



