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 bios- 
sotns 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 Bed 
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. 
183. 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. 
