SKUT. I 



MORPHOLOGY 



17 



serve as examples of this. In such cases and the leaf of the Elm 

 may be mentioned as another striking example the symmetry of 

 the individual leaf is subordinated to that of the entire plant. 



Branch Systems 



Thallophytes as well as Cormophytes exhibit systems of branching, 

 resulting either from the formation of new growing points by the 

 bifurcation of a previously existing growing point, or from the develop- 



Ma 



Fie. 10. Diagrams of branch systems. A, Dichotoinous branching ; Aa, ci|iial dichotomy ; Ab, 

 scorpioid dichotomy ; Ac, helicoid dichotomy, li, monopodial branching ; lla false dichotomy ; 

 Kb, scorpioid cyme ; Be, helicoid cyme ; ., s, sympodia. 



ment of new growing points in addition to those already present. 

 In this way there arise two systems of branching, the DiCHOTO- 

 MOUS and the MONOPODIAL. By the uniform development of a 

 continuously bifurcating stem, a typical dichotomous system of 

 branching is produced, such as is shown in Dictyota dichotoma (Fig. 8), 

 and is represented diagrammatically in Fig. 16 Ad. In a typically 

 developed example of the monopodial system there may always be 

 distinguished a persisting main axis, the MONOPODIUM, giving rise 

 to lateral branches from which, in turn, other lateral branches are 

 developed. A good example of this form of branching is afforded 

 by a Fir-tree. Where one of the two branches is regularly developed 

 at the expense of the other, the dichotomous system assumes an 



c 



