138 BOTANY AND PHARMACOGNOSY. 



situated obliquely above the last fore-leaf, usually on the frontal 

 part of the flower; the second sepal is directly behind the first 

 or diagonally opposite to it, the remaining three leaves (sepals) 

 occurring in a spiral of two-fifths (Fig. 134). Several deviations 

 from this type occur, as in Lobelia (Fig. 272), Polyala, etc. 



Two types of inflorescence are distinguished : ( i ) The in- 

 definite, in which the flowers open or develop in acropetalous 

 or centripetal succession, and (2) the definite, in which the 

 flowers open in basipetalous or centrifugal succession. The in- 

 definite type of inflorescence is seldom terminated by an ex- 

 panded flower, and two classes of this type are distinguished : 

 (a) Those in which the flowers are pedicelled, as in the raceme 

 (Fig. 139) and umbel (Fig. 169) ; and (b) in which the flowers 

 are sessile, as in the spike (Fig. 250) and head (Fig. 242). 



The RACEME is a long inflorescence with pedicelled flowers, 

 which are frequently subtended by bracts (Figs. 139, 150, and 

 207). The CORYMB is a modified raceme in wdiich the pedicels 

 of the basal flowers are much longer than those of the apical, 

 and thus the inflorescence looks like an umbel. In the milkweed 

 the flowers jiave pedicels of the same length which arise from the 

 apex of the shoot or peduncle, and this form of inflorescence is 

 known as an umbel. In the Umbelliferae a flower cluster or 

 umbellets takes the place of the individual flowers of the umbel, 

 and is known as a compound umbel (Fig. 169). 



The SPIKE is also generally a long inflorescence, the flowers 

 being sessile (Fig. 87, illus. 3), the secondary spikes in grasses 

 being known as spi relets. The spadix is a form of spike, 

 whicii is readily distinguished by the fleshy stem, in which the 

 flowers are frequently deeply imbedded, and which is frequently 

 surrounded by a large bract, the so-called spathe, as in Arisema. 

 The CATKIN is a kind of spike with small, often imperfect flowers, 

 which falls ofif as a whole, as in the staminate catkins of the 

 oak. Tlie catkins are mostly decompound, and in some species 

 of Populus the single flowers are pedicelled, and hence are 

 actually racemose rather than spicate inflorescences. 



In the head and the umbel the main inflorescential axis is 

 exceedingly short and the innermost flowers are often destitute 

 of bracts, in contrast with the external, which are frequently 



