492 PART III. THE CLASSIFICATION OF PLANTS. 



which consists of a number of capitula arranged in a raceme ; it occurs in many 

 of the Compositae, e.g. Petasites : the spicule capitiilum, which consists of 

 several spikes forming a capitulum, as in the Scirpoideas : the spicule raceme, 

 which occurs in many Grasses, in which the last branches of a compound 

 raceme are spikes. 



B. Cymose Injiore»cences : the main axis produces one, two, or more lateral 

 branches — rarely several— at the same level below its apex, which grow more 

 vigorously than the main axis, and repeat the same type of branching. 



These inflorescences are also termed dejinile because the growth of each axis 

 is arrested, by the development of a terminal flower, before that of the lateral 

 branch or branches which it bears. The simplest kind of definite inflorescence 

 is that in which the axis (peduncle) does not branch, but bears a single terminal 

 flower. 



Cymose inflorescences are also termed cenlrifagal, because the development 

 and expansion of the flowers begins with the primary axis, and occurs succes- 

 sively in the axes of the second, third, and higher orders. 



I. In the simple cyme the ramification in the secondary and higher orders 

 follows the same type. 



(a) Withoul a pseud-axis (see page 35). 



The cyme : beneath the terminal flower spring several — three or more — 

 lateral shoots of equal vigour, e.g. many Euphorbiae. This inflorescence greatly 

 resembles the true umbel, and in fact cannot be distinguished from a true 

 umbel which has a terminal flower. The identification of an inflorescence as 

 belonging to the cymose type depends in many cases on the fact that in the 

 higher orders of branching the cymes are reduced to dicbasia. 



The dichasiiim (Figs. 19 C and 20) consists of only two equal lateral shoots 

 arising at the same level below the terminal flower, and branching in a similar 

 manner. The successive false dichotomies commonly decussate, e.g. Valerian- 

 ella and the weaker inflorescences of many Euphorbia. 



(/3) Wilh a pseud-axis. 



The scorpioid cyme (cincinnus and rhipidium) : in this the lateral branches 

 occur alternately on opposite sides (Fig. 19 A and B) : Boraginaceae, Crassu- 

 laceae, Iridacero, Commelynaceae, etc. 



The helicoid cyme (bostryx and drepanium) : the lateral branches of the 

 successive ramifications always occur on the same side (Fig. 19 D) : this is 

 frequently found in Monocotyledons, such as Hemerocallis, Ornithogalum, 

 Alstroemeria, Juncaceae. 



It has been ascertained, however, that in many cases (various Solanaceae and 

 Boraginaceae) the so-called scorpioid cymes are monopodial ; the axis is there- 

 fore not a pseud-axis but a true one, and the inflorescence must be regarded as 

 a unilateral raceme. 



II. Compound cymose inflorescences arise on the one hand from the reduction 

 of the ramification in the higher orders, as, for instance, when the secondary 

 members of a cyme are not cymes, but dichasia : these are dichasial cymes ; 

 they occur in many Euphorbias : again, when dichasia terminate in scorpioid or 

 helicoid cymes. On the other hand it sometimes occurs that helicoid cymes 

 are combined to form scorpioid cymes, as in Geranium. 



C. Compound racemose and cymose inflorescences. It may occur that a com- 



