39 



is usually an involucre of bracts below the flowers. 

 The apex of the peduncle on which the flowers are 

 borne and which is really the shortened rhachis 

 is here called the receptacle of the inflorescence. 

 Small scale -like bracts are often found on the 

 receptacle subtending the individual flowers. 

 In a typical raceme there is no obvious reason why the 

 main axis should not continue to grow and produce lateral 

 branches in acropetal succession indefinitely, whereas if it soon 

 produced a terminal flower, as is the case in a cyme, its growth 

 is at once checked and the further development of the 

 inflorescence then devolves on the lateral branches. Racemose 

 inflorescences are therefore often called indeterminate, or 

 indefinite, and cymose inflorescences determinate, or definite. 

 Again if a plan is drawn of a raceme the youngest flowers are 

 in the centre and the oldest are outside, while a line following 

 the course of development from the oldest to the youngest 

 flowers of such an inflorescence passes from the outside to the 

 centre, whereas in a cyme the reverse is the case, the oldest 

 flower being in the centre. Hence racemose inflorescences are 

 called centripetal and cymose inflorescences centrifugal. In the 

 case of inflorescences in which the shoots are much reduced in 

 length and the flowers are therefore brought together more or 

 less at the same level, it is often not easy to decide to which 

 type they must be referred and the relative position of the 

 flowers then often helps us to decide the question. In a head, 

 for instance, the facts that the oldest flowers which open first 

 are on the outside and that the youngest which open last are in 

 the centre, indicate that the inflorescence is racemose. A 

 compound racemose inflorescence also is usually easily 

 recognised by the fact that there is a distinct main axis with 

 the oldest and longest branches at its base and the youngest 

 and shortest at the apex. 



The principal kinds of cymose inflorescences are : 



(a) Dichotomous cyme.. The main axis terminates in 

 a flower and two vigorous and equal lateral 

 branches develop. If there are three equally 

 vigorous lateral branches instead of two the 

 cyme becomes tricJiotomous. If this kind of 

 branching is continued and each lateral branch 

 in its turn terminates in a flower and in its turn 

 develops 2 or 3 vigorous lateral branches and 

 so on,the inflorescence becomes a compound di- 

 or tri-chotomous cyme respectively. 



