FIELDBOOK OF ILLINOIS WILD FLOWERS 



TYPES OF FLOWER CLUSTERS 



Flowers are most frequently clustered according to a definite 

 pattern. Five patterns of clusters are shown in fig. 6. The 

 spike, a, has sessile flowers attached to an unbranched stem, 

 and it may be soii^ or intnrupted. If the little flowers, or florets, 

 are closely arranged, then sparse, then packed again, the spike 

 is interrupted; with the florets in one mass the spike is solid. 

 The raceme, b, is a cluster in which the singly pediceled flowers 

 are arranged along the sides of a common stalk. The panicle, c, 

 is a compound cluster whose branches resemble racemes. In 

 the foregoing types ot clusters the order of blossoming is from 

 bottom to top of the stem, which never has a terminal flower. 



Fig. 6. — Types of inflorescence. 

 c. — Panicle, d. — Umbel, e. — Cvme. 



a. — Spike, b. — Raceme. 



In the flat-topped cluster called the umbel, d, the pedicels come 

 from the same point, the top of the peduncle, and the subtending 

 bracts become an involucre. The cyme, e, is a flat-topped cluster 

 caused by the production ot flowers in terminal buds. Hence 

 axillary buds take up the work of growth, which widens the 

 inflorescence in a compound fashion. 



SESSILE-FLORET CLUSTERS 



Three more clusters, whose florets are sessile or nearly so, 

 are the catkin, which is a nodding, drooping or rigid spike; the 

 head or receptacle bearing many flowers; and the spadix, a 

 fleshy spike or elongated head bearing small and often imperfect 

 flowers, the whole often enclosed by a large bract or modified 

 leaf known as the spathe. Typical examples are — catkin, pussy- 

 willow; head, dandelion; spathe and spadix, Jack in the pulpit. 



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