202 INDEFINITE INFLORESCENCES.—SPIKE.—AMENTUM. 
elongated axis are those that are first formed and consequently 
the oldest ; for as the axis elongates upwards it is continually 
producing other flower-buds, the age of which continues to 
decrease as we approach the growing point or apex; and as 
flower-buds are necessarily most developed in the order of their 
age, it follows that those at the base will open first, and that 
the order of expansion will proceed gradually upwards towards 
the apex, or acropetally. In the same way the flower-buds situated 
Fre, 413 Fic. 414. — 2 the circumference of a shortened 
ae) ; or dilated axis are first formed, and 
those nearest the centre or growing 
point last, and therefore their ex- 
pansion will proceed from the cir- 
cumference to the centre, or cen- 
tripetally. 
A. Kinds of Indefinite or In- 
determinate Inflorescence with an 
Hlongated Primary Azxis.—These 
are as follows :— 
a. The Spike.—This is a kind 
of inflorescence in which the ped- 
uncle is elongated and bears sessile 
flowers, or flowers in which the 
pedicels are very short, so as not 
to be clearly distinguishable. Ex- 
amples of it may be seen in the 
Rib-grass (jig. 413), and Vervain 
(fig. 414). In this kind of inflores- 
cence it will be observed that the 
flowers at the lower part of the 
spike have passed into fruit (fig. 
414), while those near the middle 
are in full flower, and those at the 
top are still undeveloped. Such an 
inflorescence exhibits therefore, ina 
Fig. 413. Spike of a species of marked degree, the acropetal order 
Rib-grass (Plantago ).—— Fig. of expansion. 
a ot Nee re There are five other kinds of 
i indefinite inflorescence which are 
simply modifications of the spike. These are the Amentum or 
Catkin, the Spadix, the Locusta, the Cone, aud the Strobile. 
b. The Amentwm or Catkin.—This is a kind of spike which 
usually bears barren flowers—that is, only staminate (fig. 415), 
or only pistillate (fig. 416) ones. The flowers of an amentum 
are also usually separated from one another by scaly bracts, and 
the whole inflorescence (at least as regards the staminate cat- 
kins) commonly falls off in one piece, soon after the process of 
flowering. The bracts have sometimes one, or at other times 
several flowers in their axils. All plants with this kind of 
