OF INFLORESCENCE. 43 



state of bracts ; but sometimes instead of two pair, we 

 find fifteen or twenty imbricated, so as to form a kind 

 of elongated spike, and in this case the flower is most 

 frequently abortive. This monstrosity is called in gar- 

 dens Dianthus Caryophyllus imbricatus. 



The pieces which form the involucra, especially those 

 in a single row, are sometimes perfectly free ; this is 

 most frequently the case : sometimes they are united 

 by their margins, so as to resemble a single leaf; such 

 are those of several kinds of Bupleurum, Seseli Hlppo- 

 marathrum, Othonna, and Nyctago. These involucra 

 are usually very inaccurately called monophyllous, which 

 term ought to be replaced by that of GaiMOPHyllous, 

 which expresses their true nature. 



When the involucra enclose several flowers, there can 

 be no doubt upon their nature ; but when they enclose 

 only one, it is often difficult to affirm if the envelope 

 be an external calyx or an involucrum : this doubt is 

 especially very great when the leaflets are united toge- 

 ther, as the sepals of a calyx. Though in the Marvel of 

 Peru the involucrum has been almost constantly taken 

 for a calyx, we are assured that it is an involucrum, 

 because in several plants of the same family this organ 

 contains several flowers, which is never the case with a 

 true calyx : the same illusion has also existed for a long 

 time in the Euphorbia, where the involucrum has been 

 called by the name of calyx, until it was known that 

 what was thought to be a single flower was an assem- 

 blage of several in a head. We know now in the same 

 manner that the spiny envelope of Chestnuts, the 

 cupule of the Acorn, or Hazel-nut, are involucra, and 

 not calyces. The question is more delicate in the 

 Malvaceae, which frequently bear, outside the calyx, a 

 row of verticillate leaflets: some call them the external 

 calyx, because they spring from the base of it. There 



