120 



BOTANY 



PART I 



the circular outline of the growing point, in which no apical cell is recognisable, 

 becomes elliptical. In the position of the foci of this ellipse the two new growing 

 points project (Fig. 139). The successive dichotomies may take place in planes at 



right angles to one another, in which case 

 the branch-system does not lie in one plane 

 as in the diagram in Fig. 82 a. 

 xiiMife mm Not uncommonly in plants of this kind 



f 



FIG. 139. Longitudinal section of a bifurcat- 

 ing shoot (p) of Lycopodium alpinum, 

 showing equal development of the rudi- 

 mentary shoots, p', p" ; b, leaf- rudiments ; 

 c, cortex ; /, vascular strands. ( x 60. 

 After HEOELMAIER.) 



FIG. 140. Sympo- 

 dium arising 

 from successive 

 dichotomies. 



FIG. 141. Bifurcating shoot 

 (p) of Lycopodium inun- 

 datum, showing unequal 

 development of the rudi- 

 mentary shoots, p', p" ; 

 6, leaf-rudiments. ( x 40. 

 After HEGELMAIER.) 



(e.g. in Selaginella] the branch-system deviates from the type described in that 

 only one of the branches of each fork grows on further and again dichotomises 

 (Fig. 140). If all the branches that in this way continue the branching are placed 

 nearly in the same direction to which the other branches stand obliquely, the 

 branch-system which results may readily be confused with racemose branching 

 (Fig. 82 &). The main axis is, however, only apparently single, each portion 

 being a daughter axis of the portion that precedes it. Such an apparent axis 

 is distinguished as a sympodium from a true main axis (monopodium), and the 

 branching is sympodial and based on dichotomy. 



All transitions from dichotomous to lateral branching are seen in the 

 Lycopodiaceae. Some species form from the outset two growing points of unequal 

 size, the smaller being soon displaced laterally in respect to the larger one (Fig. 141). 



B. Lateral Branching, (a) Place of Origin of the Lateral 

 Buds. On shoots composed of axis and leaves the lateral branches 

 as a rule occur on the axis or at the extreme base of the leaf. They 

 are usually developed at the growing point of the parent shoot in 

 acropetal succession as exogenous outgrowths of the surface in the 

 same way as the leaf primordia arise (Fig. 98 g). The positions in 

 which the lateral shoots are developed are usually strictly determined. 

 In Pteridophyta they frequently arise beside the leaf primordia, but 

 in Phanerogams, as a 'rule, where the upper side of the papilla forming 

 the young leaf passes into the tissue of the growing point, i.e. in the 

 LEAF AXIL. In some cases the branch is more on the leaf-base, in 

 others it is distinctly on the main stem. 



The primordium of a lateral branch may arise from the tissue of the axis close 

 above the leaf primordium and either after the origin of the latter (Fig. 142 /) 



