ORGANS OF REPRODtJCTION. 



195 



Fig. 400. 



h. The Corymb. — This is a kind of raceme in which the pedi- 

 cels are of different lengths, {fig. 397), viz. those, a" a", at the base 

 of the primary axis, a', longer than those towards and at the apex, 

 so that the whole form a level, or nearly level top. It occurs in 

 some species of Cerasus, the Hawthorn, &c. When the stalks 

 or secondary- axes of a corymb {fig. 398, a") instead of bearing 

 flowers immediately, divide and form tertiary, a'" a'", or other 

 axes, upon which they are placed, it is termed compound or 

 branching, as in some species of Pyrus. It sometimes happens 

 that when the flowers are first developed they form a corymb, 

 but as the primary axis elongates a raceme is produced. This 

 may be seen in many Cruciferous Plants. 



i. The Panicle. — This is a sort of compound raceme, that is to 

 say, a raceme in which the secondary axes instead of pro- 

 ducing flowers directly, branch, and form tertiary axes, &c., the 

 ultimate subdivisions of which bear the flowers {fig. 399). Ex- 

 amples of this occur in the Yucca 

 gloriosa, and in the general arrange- 

 ment of the partial inflorescences of 

 the Oat (y(^. 393). 



k. The Thyrsus or TJiyrse. — This is 

 a kind of panicle in which the pe- 

 dicels are generally very short, and 

 the whole so arranged as to form 

 a compact cluster {fig. 400). Ex- 

 amples may be found in the Horse- 

 chestnut and Lilac. 



The above kinds of indefinite in- 

 florescence all possess an elongated 

 primary axis. We now proceed to 

 describe those kinds in which the 

 primary axis is shortened or dilated 

 in various ways. 



2. Kinds of Indefinite Inflores- 

 cence with a Shortened or Dilated 

 Primary Axis. — Of these we shall 

 notice three varieties : the Capitu- 

 lum or Anthodium, the Hypantho- 

 dium, and the Umbel. 



a. The Capitulum, Anthodiu7n, or 

 Head. — This kind of inflorescence 

 constitutes the Compound Flower of Linnaeus. It is formed 

 by a number of sessile flowers crowded together on a receptacle, 

 and the whole commonly sxirrounded by an involucre. The re- 

 ceptacle, as we have seen (see page 186), may be either flattened 

 as in the Cotton Thistle (/y. 401); 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 

 02 



Fig. 400. Tliyrsns of Vine 

 (Vitis vinifera). 



