SECT. I 



MORPHOLOGY 



17 



Branch Systems 



Thallophytes as well as Cormopliytes 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- 

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

 this way there arise two systems of branching, the dichotomous and 

 the MONOPODIAL. By the uniform development of a continuously 

 bifurcating stem, a typical dichotomous system of branching is 



Fifi. 15.— Diagrams of branch systems. A, Dicliotomous branching; Au, eqnal dichotomy; Ah, 

 scorpioiil dichotomy ; Ac, helicoid dichotomy. B, monopodial branching ; Ba, false dichotomy ; 

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



produced, such as is shown in Didyota dichotoma (Fig. 8), and is 

 represented diagrammatically in Fig. 15 Aa. 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. Good 

 examples of this form of branching are afforded by many Conifers such 

 as the Onjptomeria represented in Fig. 16. Where one of the two 

 branches is regularly developed at the expense of the other, the 

 dichotomous system assumes an appearance quite different from its 

 typical form. The more vigorous branches may then, apparently, 

 form a main axis, from which the Aveaker branches seem to spring, 

 just as if they were lateral branches. This mode of branching (Fig. 



t c 



