FLOWERS : THEIR ARRANGEMENT ON THE STEM. 



61 



143 shows the plan of it. It is plainly the same as a raceme with the lower 

 pedicels much longer than the uppermost. Shorten the body, or axis, of a corymb 

 so that it is hardly perceptible, and we 

 change it into 



178. An Umbel, as in Fig. 144. This is a 

 cluster in which the pedicels all spring from 

 about the same level, like the rays or sticks 

 of an umbrella, from which it takes its name. 

 The Milkweed and Primrose bear their 

 flowers in umbels. 



179. The outer blossoms of a corymb or 

 an umbel plainly answer to the lower blos- 

 soms of a raceme. So the umbel and the 

 corymb blossom from the circumference 



towards the centre, the 

 outer flower-buds being 

 the oldest. By that we 

 may know such clusters 

 from cymes. '" 



180. A Head is a flower- 

 cluster with a very short body, or axis, and without any pedi- 

 cels to the blossoms, or hardly any, so that it has a rounded 

 form. The Button-bush (Fig. 145), the Thistle, and the Eed 

 Clover are good examples. 



181. It is plain that an umbel would be changed into a head 

 by shortening its pedicels down to nothing ; or, contrarily, that 

 a head would become an umbel by giving stalks to its flowers. 



182. A Spike is a lengthened flower-cluster, with no pedicels to 

 the flowers, or hardly any. Fig. 141 gives the plan of a spike; 

 and the common Mullein and the Plantain are good examples. 

 A head would become a spike by lengthening its axis. A ra- 

 ceme would become a spike by shortening its pedicels so much 

 that they could hardly be seen. The Catkin and the Spadix are 

 only sorts of spike. 



] 83. A Catkin or Ament is a spike with scaly bracts. The flowers of the Wil- 

 low, Poplar, Alder, and Birch (Fig. 146) are in catkins. 



