82 ELEMENTS OF STBUCTliRAL BOTANY. 



onec iu Sliepberd's-Purse, the order of developement is 

 from the outside towards the centre. 



121. If you now look at your Buttercup, you will be at 

 once struck with the difference of plan exhibited. The 

 main axis or stem has a flower on the end of it, and its 

 further growth is therefore checked. And so in like 

 manner, from the top downwards, the growth of the 

 branches is checked b}'^ the production of flowers at their 

 extremities. The mode of inflorescence here displayed 

 is definite, or determinate, or terminal. It is also 

 called centrifugal, because the developement of the 

 flowers is the reverse of that exhibited in the first mode. 

 The upper, or, in the case of close clusters, the central 

 flowers open first. In either mode, if there is but one 

 flower in each axil, or but one flower at the end of each 

 branch, the flowers are said to be solitari/. 



122. Of indeterminate inflorescence there are 

 several varieties. In Slicpherd's-Purse we have an 

 instance of the raceme, which may be described as Tj 

 cluster in which each flower springs from an axil, and 

 is supported on a pedicel of its own. If the pedicels 

 are absent, and the flowers consequently sessile in the 

 axils, the cluster becomes a spike, of which the common 

 Plantain and the Mullein furnish good examples. The 

 catkins of the Willow (Figs. 63, 64) and Birch, and the 

 spadix of the Indian Turnip (Figs. 80, 81) are also 

 spikes, the former having scaly bracts and the latter a 

 fleshy axis. If you suppose the internodes of a spike 

 to be suppressed, so that the flowers are densely 

 crowded, you will have a head, of which Clover and 

 Button-bush supply instances. If tlie lower pedicels 

 of a raceme are considerably longer than the upper 

 ones, so that all the blossoms are nearly on the same 



