nnt aval Family of Phiiiis called Composilce. 93 



Tlie absolute constancy in the order of expansion of the simple 

 capituluni from circumference to centre, and the more or less 

 complete inversion of this order in the compound capitulum, ap- 

 pear to afford tests of the real structure in certain cases where 

 the degree of composition, and consequently the proper names of 

 some of the parts, might otherwise be doubtful. 



To illustrate this I select two genera, Lagasca and CcEsulia. 



In Lagasca the capitulum, lK)th from its form and the appear- 

 ance of its involucrum, mioht at first sio;ht be considered as sim- 

 pie : on cxaifiination, however, it is found to differ from all simple 

 capitula, in each floret being furnished with a tubular envelope, 

 exactly resembling a five-toothed perianthium, but which does 

 not in any state cohere with the included ovarium. 



Cavanilles, by whom the genus was established, regarded this 

 envelope as a genuine perianthium, and erroneously described its 

 tube as cohering with the ovarium ; an error which is copied in 

 Persoon's Synopsis Plantaruni, where the genus is consequently 

 placed in Polygamia fequalis. Jacquin, who has published La- 

 gasca under the name of Nocccea mollis*, also describes the en- 

 velope of each flower as a j)roper perianthium, although aware 

 of its tube being distinct from the ovarium. Subsequent writers 

 liave, indeed, more correctly referred the genus to Polygamia 

 segregala; but the terms involucellum and calyculus, which they 

 apply to the envelope in question, appear to me objectionable, 

 for a reason that will presently be given. 



Three suppositions may be formed respecting the nature of this 

 envelope, namely, either that it is an involucrum reduced, as in 

 Echiuops, to a single flower ; secondly, that it is a proper perian- 

 thium, which in appearance it very much resembles; or thirdly, 



» Fragm. Bot. p. 5S. tab. 85. 



that 



