6.] 



CHAPTER I. GENERAL MORPHOLOGY. 



35 



systems is limited by the formation of a terminal flower; but 

 the terminal flower is developed last at the apex of the main 

 axis ; hence it grows for a longer period than the lateral axes, 

 although, as is commonly the case, the rapidity of the growth of 

 the lateral axes may have been greater than that of the main 

 axis. 



5. Cymose branching. The characteristic feature of a cymose 

 branch-system is the absence of a main axis. This is due to the 

 diminished rapidity, or shorter duration, of the growth of the 

 branching member as compared with that of the lateral members. 

 When a main axis is formed, it is a pseud-axis, that is, it is not 

 produced by the continuous elongation of one and the same 

 member, but is built up from segments of axes of different orders. 

 Such a pseud-axis is termed a sympodium. 



a. No pseud- 

 axis is formed 

 when two or 

 more lateral 

 .axes elongate 

 with equal 



vigour, 



and 



more vigor- 

 ously than 

 the primary 

 axis. When 

 the number 

 .of vigorous 

 lateral axes 

 happens to 

 be two, the 

 branch - sys- 

 tem bears a 



superficial resemblance to a true dichotomy, and is hence termed 

 a false dichotomy, or dichasium (Fig. 19 0; Fig. 20). When 

 many lateral axes are developed close together, the branch-system 

 is termed a pleiochasium. 



If the dicJiasial branching be repeated, the various dichasia 

 may lie in one plane (as in the Mistletoe) ; or, as is more frequently 

 the case, in different planes. Examples are afforded by the in- 

 florescences of the Spurges (Euphorbia) ; the branches of the 

 Lilac (Syringa), in which usually the terminal bud dies, and the 



FIG. 20. Diagram of a False Dichotomy or Dichasium ; the Roman 

 numerals indicate the order of development of the shoots of the 

 system. Those numbered II' and II'' are equally vigorous, and 

 much more so than the primary axis I. (From Sachs.) 



