raceme, corymb
A raceme is an inflorescence bearing pedicelled (stalked) flowers on a common, elongated peduncle. The flowers develop acropetally (from the bottom up), so the youngest flowers are those closest to the apex.
FIG. 200 (left). Raceme, with a general peduncle (P), pedicels (p), bracts (b) and bractlets (b') 1
A corymb is the same as a raceme, except that it is flat and broad, either convex or flat-topped. That is, a raceme becomes a corymb by lengthening the lower pedicels while the uppermost remain shorter.1
FIG 202. A corymb.1
1. Gray. A. 1887. The elements of botany for beginners and for schools. New York & Chicago: American Book Company, pp 74-76.
See Position and Arrangement of Flowers, or Inflorescence from Gray's Elements of Botany for more about inflorescences.