310 COMA INVOLUCRE. [BOOK i. 



even from the leaves of the stem. In fact, there is in many 

 cases no other mode than ascertaining the usual number of 

 sepals in other plants of the same natural order, and con- 

 sidering every leaf-like appendage on the outside of the usual 

 number of sepals as a bract. In Camellia, for example, if it 

 were not known that the normal number of sepals of kindred 

 genera is five, it would be impossible to determine the num- 

 ber of its sepals. When the bracts are very small, they are 

 called bractlets (bracteolce) ; or, if they are of different sizes 

 upon the same inflorescence, the smallest receive that name. 

 It rarely occurs that an inflorescence is destitute of bracts. 

 In Crucifers this is a general character, and is observed by 

 Link to indicate an extremely irregular structure. When 

 bracts do not immediately support a flower or its stalk, they 

 are called empty (vacua) . As a general rule, it is to be under- 

 stood, that whatever intervenes between the true leaves and 

 the calyx, whatever be their form, colour, size, or other pecu- 

 liarity, comes within the meaning of the term. 



Under particular circumstances bracts have received the 

 following peculiar names : 



When they are empty, and terminate the inflorescence, 

 they form a coma, as in Green and purple Clary (Salvia 

 Horminum), and in the common Pine Apple or Ananas. In 

 such cases they are often enlarged and coloured. 



If they are verticillate, and surround several flowers, they 

 constitute an involucre. In Umbelliferous plants, the bracts 

 which surround the general umbel are called an universal 

 involucre ; and those which surround the iimbellules a partial 

 involucre, or involucel. 



In Composites, the involucre often consists of several rows 

 of imbricated bracts, and has received a variety of names, for 

 none of which there appears to be occasion. Linnaeus called 

 it calyx communis, Necker perigynandra communis, Richard 

 periphoranthium, Cassini periclinium. There is often found at 

 the base of the involucre of Composites an exterior rank of 

 bracts, which Linnseus called calyculus ; and such involucres 

 as were so circumstanced calyx calyculatus. Cassini restricted 

 the term involucre to this ; but it seems most convenient to 



