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 so/id or interrupted. 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 1s 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 of clusters the order of blossoming 1s from 
bottom to top of the stem, which never has a terminal flower. 
Fig. 6—Types OF INFLORESCENCE. a.—Spike. b.—Raceme. 
c.—Panicle. d.—Umbel. e.—Cyme. 
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 of 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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