204 



ORGANOGBAPHT. 



ceptacle, and the whole surrounded by an involucre. The re- 

 ceptacle as we have seen (see page 193) may be either flattened 

 as in the Cotton Thistle (^^i. 404); or slightly convex, as in 

 the Dandelion; or conical, as in the Chaniomile {fig. 381); or 

 globular, as in the American Button Bush; or elliptical, &c., 

 by which a A^ariety of forms is given to the heads of flowers. 

 This kind of indefinite inflorescence, as well as all others with 

 shortened or dilated primary axes, also exhibit a centripetal 

 order of expansion. This may be well seen in the capitulum 

 of the Scabious {fig. 405), where the outer flowers, (or florets 

 as they are commonly called from their smallness), are fully ex- 

 panded, those within them less so, and those in the centre in an 

 unopened condition. Here therefore the order of expansion 

 is towards the centre — that i>, centripetally. 



b. The Hypanthodium. — This kind of inflorescence is biit a slight 

 modification of the last. It is formed by a receptacle which is 

 usually of a fleshy nature becoming more or less incurved, and 

 thus partially, as in the Dorstenia {fig. 384), or entirely, as in 

 the Fig {fig. 383), enclosing the flowers which it bears upon its 

 surface. The flowers m this kind of inflorescence are usually 

 unisexual, and there is no involucre to them as in the true 

 Capitulum. 



Fig. 405 



Fig. 406. 



7V<7. 40.J. Cnpitnliim of Sca- 

 iiious USciibiosa). Tlie 

 outermost florets may be 

 observed to be more ex- 



))aii(led than the inner 



J-'ig. 4{)G. Simple umbel of 

 a species of Allium. 



c. The Umbel. — Wlicn the ])rimary axis is shortened, and 

 gives ofl" from its apex a nuinl)er of secondary axes or pedicels 



