[Illustration: Fig. 451. Head of sunflower showing centripetal inflorescence of tubular flowers. (Photo by the Author.)] =828. Anthesis of flowers with indeterminate inflorescence.=—In the anthesis of the raceme as well as in other corymbose forms the lower (or outer) flowers being older, open first. The opening of the flowers then takes place from below, upward; or from the outside, inward toward the center of inflorescence. The _anthesis_, i.e., the opening of the flowers of corymbose forms is said to be _centripetal_, i.e., it progresses from outside, inward. The anthesis of the fuller’s teazel is peculiar, since it shows both types. There are several distinct advantages to the plant where anthesis extends over a period of time, as it favors cross pollination, favors the formation of seed in case conditions should be unfavorable at one period of anthesis, distributes the drain on the plant for food, etc. [Illustration: Fig. 452. Heads of fuller’s teazel in different stages of flowering.] B. FLOWER CLUSTERS WITH DETERMINATE INFLORESCENCE. =829. The simplest mode of determinate inflorescence= is a plant with a solitary terminal flower, as in the hepatica, the tulip, etc. The leaves in these two plants are clustered in the form of a rosette, and the aerial shoot is naked and bears the single flower at its summit. Such a flower-shoot is a _scape_. As in the case of the indeterminate inflorescence, so here the larger number of flower-shoots are more complex and specialized, resulting in the evolution of flower clusters or masses. Accompanying the association of flowers into clusters there has been a reduction in leaf surface on the flower-shoot so that the flowers predominate in mass and are more conspicuous. Among the recognized modes of determinate inflorescence, the following are the chief ones: =830. The cyme.=—In the cyme the terminal flower on the main axis opens first and the remaining flowers are borne on lateral shoots, which arise from the axils of leaves or bracts, below. These lateral shoots usually branch and elongate so that the terminal flowers on all the branches reach nearly the same height as the terminal flower on the main shoot, forming a somewhat flattened or convex top of the flower cluster. This is illustrated in the basswood flower. The anthesis of the cyme is _centrifugal_, i.e., from the inside outward to the margin. But it is often more or less mixed, since the lateral shoots if they bear more than one flower are diminutive cymes and the terminal flower opens before the lateral ones. Where the flower cluster is quite large and the branching quite extensive, _compound cymes_ are formed, as in the dogwood, hydrangea, etc. [Illustration: Fig. 453. Diagrams of cymose inflorescence. _A_, dichasium; _B_, scorpioid cyme; _C_, helicoid cyme. (After Strasburger.)]