Origin and Development of the Composite. 
ti 7 
would tend to be conical and elongated with the subtending bracts 
of the flowers reduced but still present (cp. Fig. 19, A-B). 
In a racemose umbel the flowers are usually already crowded 
together. The food supply is already reduced, so that the flowers 
are small, and, as the outer flowers receive more illumination, they 
tend to become zygomorphic (cp. Goebel, V, 21, p. 552). The 
pedicels at their insertion on the peduncle are much more crowded 
than the florets at the top of the umbel, so that the bracts of all 
except the outer flowers have already become reduced or have 
disappeared completely. If abortion of the pedicels occurred the 
florets would then be sessile on a more or less flat receptacle with 
very reduced bracts to the inner florets or no inner bracts at all. 
The bracts of the outer florets would form a structure corres¬ 
ponding to the pericline of Cassini (cp. Fig. 19, C-D). 
Fig. 19. Origin of the Capitulum. A—spike ; B—capitulum derived from 
spike ; C—racemose umbel; D—capitulum derived from racemose umbel. 
Parkin (10), although he does not discuss the evolution of the 
involucre at all and makes only a passing reference to the origin of 
the capitulum, gives a diagram (op. cit. PI. 18) in which the spike is 
regarded as a side line and the head as derived from the simple 
raceme via the corymb and the umbel. Masters (IV, 52) records 
anomalous elongation of the pedicels in Hypochceris radicata and 
Senecio vulgaris , etc., by which change “ the capitulum assumes the 
appearance of a simple umbel.” 
The involucrate inflorescence occurs as a normal form in quite 
a number of families, e.g., Dipsaceae, Umbelliferae, Cornaceae, 
Proteaceae and Eriocaulaceae, and in many others as an exceptional 
