DEVELOPMENT OF THE MEMBERS OF A BRANCH-SYSTEM. 



179 



II' 

 Hi 



or cymose manner; and the cymose development may be either apparently 

 dichotomous (or even apparently polytomous) or sympodial. 



(a) A racemose system occurs when the monopodial mother-shoot continues 

 to develope more strongly than all the lateral shoots, and when the lateral shoots 

 of each successive order behave in the same manner in respect to their mother- 

 shoot. This occurs very clearly, for instance, in the stems of most Conifers 

 (especially Pinus, Araucana, &c.) and in the compound leaves of Umbellifers. 



(b) The cymose development of a monopodial system, or a Cyme, depends on 

 the fact that each lateral shoot begins from an early period to grow more strongly, 

 and in consequence of this, also branches more copiously than the mother-shoot, 

 the growth of which then usually soon ceases. Two principal forms of Cyme 

 may be distinguished, according as a pseud- axis (sympodium) is formed or not. 



(a) When two, three, or more lateral shoots arise beneath the growing end of 

 each shoot, which develope 

 in different directions more 

 strongly than their mother- 

 shoot, the growth of which 

 soon ceases, a false Dicho- 

 tomy (or Trichotomy, or 

 Polytomy) arises. Fig. 135 

 represents the formation of 

 a false dichotomy; the shoot 

 / produces the shoots // , 

 //'', originally weaker, but 

 soon growing more strong- 

 ly, while the growth of / 



eases; the same takes place 



ith T//", and ///'^ False 



ichotomies of this kind, which occur abundantly in the inflorescences of Phanero- 

 gams, are termed by Schimper Dichasia, But instead of two lateral branches 

 growing out in opposite directions, three or more shoots standing in a true 

 or spurious whorl may develope more strongly than their mother-shoot, and 

 thus arises an umbellate system, such as is developed in a typical manner in the 

 inflorescences of our native Euphorbias; a system of this kind may be called a 

 Cymose Umbel. 



(/3) The sympodial development of an originally monopodial system occurs 

 when one lateral shoot always developes with greater vigour than its mother- 

 shoot, as is shown in Fig. 136, A, where the lateral shoot 2, 2 grows more 

 strongly than the part 2,1 of its mother-shoot, and so on. 'Usually the portions 

 of all the shoots which lie below their lateral branches develope more strongly 

 than the terminal portions, as is indicated in the figure by the thicker lines ; the 

 terminal portions (indicated by thin lines) often die off early; the thicker basal 

 portions of the different ramifications which proceed from one another then com- 

 monly place themselves in a straight line, and have the appearance of a connected 

 whole ; like a primary shoot to which the terminal portions of each separate order 

 of shoots are attached as if they were lateral branches. The apparent primary 



N 2 



Fig. 135.— Diagram of a false dichotomy (dichasium) ; the numerals Indicate the order 

 of development of the shoots of the system. 



