42 VEGETABLE ORGANOGRAPHY. 



foliaceous appearance, assumes either that of a spiny 

 point, (as in Barleria, Exoacantha, &c.) or of a small 

 tendrill, (as in some species of Bauhinia,) or of a 

 tubercle or gland. 



As long as the bracts are, by the disposition of the 

 flowers, so separated from one another as not to form a 

 ring or particular envelope, the name of bracts is 

 applied to them ; but they take another appearance when 

 the near approach of the pedicels or peduncles compels 

 the branches to arise in more or less regular verticils, as 

 is seen in umbels, corymbs, and. capitula ; the name of 

 Involucrum is then given to them collectively, and to 

 each individually the names of Scale, Leaflet, or Bract. 



In umbels, where the common pedicule is not dilated 

 into a receptacle, the involucra are generally composed 

 of as many bracts as there are rays in the umbel; and 

 they are distributed in a single row. 



In flowers in a compact head, the number of the 

 leaflets of the involucrum is rarely fixed ; they form 

 around the flowers an envelope of one or several rows, 

 which surround them so closely that it seems as if all 

 the flowers of a head formed but one, the involucrum 

 appearing to be a calyx. 



The bracts which compose the involucra may be 

 either verticillate in a single row ( uniseriales ) , or in 

 two (biseriales), or in several ( pluriseriales ) \ When 

 they are in two rows, and the outside one is perceptibly 

 smaller, the involucrum is said to be Caliculate, or 

 furnished at its base with a kind of small calyx : when 

 they are in several rows, and the outer ones cover over 

 the base of the inner ones, gradually diminishing in 

 size, the involucrum is said to be Imbricate. A sin- 

 gular mode of imbrication is accidentally presented in 

 some Pinks : their flower, in the natural state, is fur- 

 nished at the base with two pair of leaves reduced to th^ 





