Fig. 218.—Remains of a Last Year’s Umbel of Wild Carrot.
Centrifugal or Determinate Clusters.—When the terminal or central flower opens first, the cluster is said to be centrifugal. The growth of the shoot or cluster is determinate, since the length is definitely determined or stopped by the terminal flower. Fig. [219] shows a determinate or centrifugal mode of flower bearing.
Fig. 219.—Determinate or Cymose Arrangement.—Wild geranium.
Dense centrifugal clusters are usually flattish on top because of the cessation of growth in the main or central axis. These compact flower-clusters are known as cymes. Centrifugal clusters are sometimes said to be cymose in mode. Apples, pears (Fig. [220]), and elders bear flowers in cymes. Some cyme-forms are like umbels in general appearance. A head-like cymose cluster is a glomerule; it blooms from the top downwards rather than from the base upwards.
Mixed Clusters.—Often the cluster is mixed, being determinate in one part and indeterminate in another part of the same cluster. The main cluster may be indeterminate, but the branches determinate. The cluster has the appearance of a panicle, and is usually so called, but it is really a thyrse. Lilac is a familiar example of a thyrse. In some cases the main cluster is determinate and the branches are indeterminate, as in hydrangea and elder.
Fig. 220.—Cyme of Pear. Often imperfect.
Inflorescence.—The mode or method of flower arrangement is known as the inflorescence. That is, the inflorescence is cymose, corymbose, paniculate, spicate, solitary, determinate, indeterminate. By custom, however, the word “inflorescence” has come to be used in works on descriptive botany for the flower-cluster itself. Thus a cyme or a panicle may be called an inflorescence. It will be seen that even solitary flowers follow either indeterminate or determinate methods of branching.
