80 



AKRANGEMENT OF FLOWERS ON THE STEM. [LESSON 11. 



2Q7. The Spiika, This is a flower-cluster with a more or less 

 lengthened axis, aloag which the flowers are sessile or 

 nearly so; as in the Mullein and the Plantain (Fig. 160). 

 It is just the same as a raceme, therefore, without any 

 pedicels to the flowers. 



208. The Head is a round or roundish cluster of flowers 

 which are sessile on a very short axis or receptacle, as in 

 the Button-ball, Button-bush (Fig. 161), and Red Clover. 

 It is just what a spike would become if its axis were 

 shortened; or an umbel, if its pedicels were all shortened 

 until the flowers became sessile or apparently so. The 

 head of the Button-bush (Fig. 161) is naked ; but that of 

 the Thistle, of the Dandelion, the Cichory (Fig. 221), 

 and the like, is surrounded by empty bracts, which form 

 an involucre. Two particular forms of the spike and the 

 head have received particular names, namely, the Spadix. 

 and the CcUMn. 



209. A Spadix is nothing but a fleshy spike or head, with smaU 

 and often imperfect flowers, as in the Calla, the Indian Turnip 



(Fig. 162), Sweet Flag, &c. It is commonly covered by a peculiar 

 enveloping leaf, called a spaihe. 



FIG. 160.. Spike of tlie common Plantain or Ribwort. 



FIG. 161. Head of the Button-bush (Cophalanthus). 



FIG. 163. Spadix and spathe of the Indian Turnip j the latter cut through below. 



