142 PRACTICAL COURSE IN BOTANY 
161. Indeterminate inflorescence is always axillary, 
since the production of a terminal flower would stop further 
growth in that direction and thus terminate the development 
of the axis. The raceme is the typical 
flower cluster of the indefinite sort. In 
such an arrangement the oldest flowers 
are at the lower nodes, new ones appear- 
ing only as the axis lengthens and pro- 
duces new internodes. The little scale or 
bract usually found at the base of the pedi- 
cel in flower clusters of this sort is a re- 
duced leaf, and the fact that the flower 
stalk springs from the axil shows it to be 
of the essential nature of a branch. 
When the flowers are sessile and crowded 
on the axis in various degrees, the cluster 
Pic. 167.— Raceme Produced may be a spike, as seen in the 
of milk vetch (Astraga- plantain, knotweed, etc., or a head, like 
lus). 
that of the clover, buttonwood, and syca- 
more. The catkins that form the characteristic inflorescence 
of most of our forest trees are merely pendant spikes. The 
corymb is a modification 
of the raceme in which 
the lower pedicels are 
elongated so as to place 
their flowers on a level 
with those of the upper 
nodes, making a convex, 
or more or less flat- 
topped cluster, as in the 
wall-flower and haw- 
thorn. The umbel dif- 
fers from the corymb in 
having the pedicels with 
their bracts all gathered ae 
at the top of the pe- Fia. 168. — Catkins of aspen. 
