DEVELOPMENT OF THE MEMBERS OF ONE BRANCH-SYSTEM, 



157 



or the bud-condition of the branch-system. Not unfrequently the original cha- 

 racter is maintained in their further growth, not only in dichotomous but also 

 in monopodial systems. The two bifurcations develope, in the case of dicho- 

 tomy, with equal strength and branch uniformly ; in the case of a monopodium the 

 primary axis continues to grow more strongly than all the secondary axes, and 

 branches more luxuriantly. But it is very commonly the case that in a dichotomous 

 system single bifurcations grow more weakly, or that in a system which starts on 

 a monopodial plan some of the lateral axes, soon after their formation, grow more 

 strongly and branch more luxuriantly than the primary axis. In such cases the 

 original character of the branch-system becomes less and less evident as it de- 

 vclopes ; and it ma}' happen that systems originally dichotomous have subsequently 

 the appearance of monopodia, and vice versa. It is therefore impossible to infer, 

 without further evidence, the original form of a branch-system from its mature 

 condition. It cannot be inferred from a maturely developed system whether it 

 originated in dichotomy or in lateral branching. It will therefore be desirable to 

 make here a simple classification of the most important changes which a branch- 

 system undergoes during the development of its members. 



(i) The Dr^elopmctit of Dichotomous Systems may take place either in a forked 

 or a sympodial manner ; I call a S}stem 

 forked when at each bifurcation the two 

 branches develope with equal strength, as 

 in Fig. 126, A. The dichotomous system 

 is developed sympodially when at each bifur- 

 cation one branch developes more strongly 

 than the other ; in this case the base of each 

 successive bifurcation forms apparently a 

 primary shoot, on which the weaker branches 

 appear as lateral shoots (Fig. 126, B, C). 

 The apparent primary shoot, which in fact 

 consists of the bases of consecutive bifurca- 

 tions, may on this account be termed a Pseud- 

 axis or Sympodium ^ Thus in B (Fig. 126) 

 the sympodium is composed of the left-hand 

 branches ///; in C of the alternate left and 

 right-hand branches / r, I r. Whether the 

 case represented in B, which, on account of 

 its similarity to certain monopodial systems, 

 may be termed a Helicoid (bostrychoid) Dichotomy, actually occurs is doubtful 

 (probably however in the leaf of Adia?itum pedatiwi). On the other hand the 

 development represented in Fig. 126, C, is common in shoots of Selaginella, 

 and, on account of its resemblance to some monopodial systems, may be termed 

 a Scorpioid (cicinal) Dichotomy-. 



Fig. 126.— Diagram of the various modes of develop- 

 ment of a dichotomy ; A one developed by bifurcation ; 

 B a helicoid ; C a scorpioid dichotomy. 



* In opposition to the view expressed in my first edition, I now consider it more convenient 

 to apply the term Sympodium only to the pseud-axis itself, and not to the whole branch-system ; 

 and the same in the originally monopodial systems. 



- On Dichotomous Inflorescences cf. Book II. Phanerogams. 



