CAPITULUM OR HEAD. 207 
ment of the partial inflorescences of the Oat (fig. 419). When 
the panicle is much branched and the flowers placed on short 
pedicels, so that the whole inflorescence forms a compact cluster 
of a somewhat pyramidal form, as in the Lilac and Vine, it is 
sometimes termed a thyrsus or thyrse (fig. 426). 
B. Kinds of Indefinite Inflorescence with a Shortened or Dilated 
Primary Axis.—Of these we distinguish two varieties :—the 
Capitulum or Anthodium, and the Umbel: 
a. The Capitulum, Anthodiwm, or Head.—This inflorescence 
was formerly called a Compound Flower ; and its involucre a 
Common Calyx. Its constituent flowers from their small size are 
commonly termed florets. This inflorescence is usually formed 
Fic. 426. 
Fic. 427. 
Fig, 426, Thyrsus of Vine (Vitis vinifera).——Fig. 427, Capitulum of Cotton 
Thistle (Onopordum Acanthium), 
by a number of sessile florets crowded together on a receptacle, 
and the whole surrounded by an involucre (fig. 399) ; but in some 
cases the florets are but few in number, and in other capitula the 
involucre is absent. The receptacle, as we have seen (page 198), 
may be either flattened, as in the Cotton Thistle (fig. 427) ; or 
slightly convex, as in the Dandelion; or conical, as in the 
Chamomile; or globular, as in the American Button-bush ; 
or elliptical, &c., by which a variety of forms is given to the 
different capitula. 
This kind of indefinite inflorescence, as well as all others 
in this division with shortened or dilated primary axes, also 
exhibit a centripetal order of expansion. This may be well 
seen in the capitulum of the Scabious (jig. 428), where the outer 
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