SECTION 8.] 



INFLORESCENCE. 



75 



which are sessile on a very short axis or receptacle, as in the Button-ball, 

 Button-busb (Fig. 205), and Red Clover. It is just wliat a spike would 



become if its axis were shortened ; or an nmbel, if its pedicels were all 



shortened until tlie flowers became sessile. The head 



of the Button-bush is naked; but that of the Thistle, 



of the Dandelion, and the like, is surrounded by empty 



bracts, wliich form an Involucre. Two particular forms 



of the spike and the head have received particular 



names, namely, the Spadix and the Catkin. 



212. A Spadix is a fleshy spike or head, with small 

 and often imperfect flowers, as in the Calla, Indian 

 Turnip, (Fig. 206), Sweet Flag, etc. It is commonly 

 surrounded or embraced by a peculiar enveloping leaf, 

 called a Spathe. 



213. A Catkin, or Ament, is the name given to the 

 scaly sort of spike of the Birch (Fig. 207) and Alder, 

 the Willow and Poplar, and one sort of flower-clusters 

 of the Oak, Hickory, and the like, — the so-called Amen- 

 taceous trees. 



214. Compound flower-clusters of these kinds are 

 not uncommon. Wiien the stalks which in the sim- 

 ple umbel are the pedicels of single flowers themselves 

 branch into an umbel, a Compound Umbel is formed. 



Fio. 205. Head of the Button-bush (Cephalanthus). 



Fio. 206. Spadix and spathe of the Indian Turnip ; the latter cut through below. 



FlQ. 207. Catkin, or Ament, of Birch. 



