182 



DEFINITE INFLOEESCENCE. 



Thus we may have a group of racemes arranged in a racemose manner, 

 on a common axis forming a raceme of racemes or a compound raceme, 

 as in Astilbe. In the same way we may have compound umbels, as 

 in Hemlock and most Umbelliferse (fig. 262), a compound spike, as 

 in Eye-grass, a compound spadix, as in some palms, and a compound 

 capitulum, as iu the Hen-and-Chickens Daisy. Again, there may be 

 a raceme of capitula, that is, a group of capitula disposed in a race- 

 mose manner, as iu Petasites, a raceme of umbels as in Ivy, and so 

 on, aU the forms of inflorescence being indefinite in disposition. 



On reviewing these difiierent kinds of inflorescence, it will be 

 observed that the elongation or shortening of the axis, and the pre- 

 sence or absence of stalks to the flowers, determine the different 

 varieties. Thus, a spike is a raceme in which the flowers are not 

 stalked, the umbel is a raceme in which the primary axis is shortened, 

 the capitulum or head is a spike in which the same shortening has 

 taken place. 



Definite Inflokescence. — The simplest form of this inflores- 

 cence is seen in Anemone nemorosa (fig. 268), or in Gentiana acaulis 



(Gentianella), where the axis termi- 

 nates in a single flower ; and if other 

 flowers are produced, they arise from 

 the leaves below the first-formed 

 flower. The general name of Cyme 

 is applied to the arrangement of a 

 group of flowers in a definite inflor- 

 escence. It is sometimes difficult to 

 understand the mode of development 

 or evolution of the flowers in such 

 an inflorescence, if the axes are much 

 contracted, and the flowers them- 

 selves are numerous. It may be 

 distinctly traced, however, in plants 

 with opposite leaves, in which the 

 difierent axes are clearly developed. 

 In fig. 269 is represented the flower- 

 ing branch of Ery thr«a Centaurium. Here the primary axis, a, ends in 

 a flower, /', which has passed into the state of fruit. At its base two 

 leaves are produced, each of which is capable of developing buds. 

 These are flower-buds, and constitute secondary axes, a a, ending in 

 single flowers, /"/", which are thus terminal and solitary; and at 



Fig. 269. Flowering branch of Biythraea Centaurium. a', Primary axis, a" a". Two 

 secondary axes, a'" a!" a'", Tertiary axes, four in number, a"" a"" a"". Quaternary axes, 

 eight in number. The flowSrs are shown in various stages of development. /', Solitary flower 

 which has passed into fruit, terminating the primary axis. /", Flowers less advanced, ter- 

 minating the secondary axes. /'", Flowers in bud at the extremity of the tertiary axes, and 

 so on. Inflorescence definite or determinate. Evolution of flowers centrifugal. 



Fig. 269. 



