230 



FLOWERS AND THEIR WORK. 



The order of flowering usually follows the order of 

 development, and hence the order of flowering in racemes is 

 centripetal, whereas that of cymes is centrifugal. In the 

 first case the youngest flowers are nearest the apex (in a long 

 inflorescence) or the centre (in a flat- or round-topped inflor- 

 escence). In the second case the youngest flowers are nearest 

 the base or outside of the inflorescence. 



The simplest type of raceme consists of an elongated axis or 

 peduncle which bears stalked flowers (stalks about equal in length), 



e.g. Foxglove, Hyacinth. If 

 the branches of the parent 

 axis branch again so that 

 each secondary axis bears 

 several blossoms instead of 

 one, we have what is known 

 as the compound raceme or 

 panicle. This is the most 

 primitive type of inflores- 

 cence, for it is really the 

 modified upper region of the 

 plant, whereas the simple 

 raceme is more highly differ- 

 entiated and has become 

 simple by reduction. Many 

 terms have been applied to 

 racemose inflorescences which look peculiar at first sight, but on 

 further observation are seen to differ in small details only. The 

 more important of these are (1) Corymb: axis elongated, flower- 

 stalks unequal in length, bringing the flowers to about the same 

 level (Fig. 78, Candytuft) ; (2) Spike : axis elongated, flowers sessile 

 (Plantain, Orchids) ; (3) Catkin : a spike bearing unisexual flowers 

 of one kind (Willow, Hazel) ; (4) Spadix : 

 a spike with fleshy axis, usually bearing 

 unisexual flowers, enclosed by a large 

 bract, the spathe (Arum) ; (5) Simple 

 umbel: axis shortened, flowers stalked 

 (Fig. 79, Cherry) ; (6) Capitulum ; axis 

 shortened and expanded, flowers sessile 

 (Composites). 



Cymose inflorescences are those in 

 which the axis ends in a flower after 

 bearing one, two, or more daughter-axes, 



each of which may repeat the process. The daughter-axes may come 

 off singly (uniparous cyme) e.g. Forget-me-not and other Borages, 

 Sundew ; or in opposite pairs (biparous cyme) e.g. Stitchwort and 

 Campion Family, Red and Yellow Gentians; or in whorls of three 

 or more (multiparous cyme) e.g. Elder. 



Examine and sketch the various kinds of flat-topped inflorescences 



Fig. 78. A Corymb. 



Fig. 79. A Simple Umbel 



