178 



INDEFINITE INI'LOEESCENCE. 



d". The development in each of the secondary axes is centripetal, 

 h hhh being the bracts from which the separate axes are produced. 

 If in a raceme the lower flower-stalks are elongated, and thus all the 

 flowers are nearly on a level, a corymb is formed, which may be simple, 

 as in fig. 256, where the primary axis, a, divides into secondary axes, 

 a" a', which end ia single flowers ; or branching, as in fig. 257, where 

 the secondary axes again subdivide. 



Fig. 268. 



Fig. 259. 



Fig. 260. 



If the peduncles or secondary axes are very short or awanting, so 

 that the flowers are sessile, a spike is produced, as in Plantago and 

 Verbena officinalis (fig. 258). The spike sometimes bears unisexual 

 flowers, usually staminiferous, the whole falling off by an articulation, 

 as in Willow or Hazel (fig. 259), and then it is called an amentum or 

 catldn ; at other times it becomes succulent, bearing numerous flowers 



Fig. 25S. Spike of Verbena officinalis, showing sessile flowers on a common rachis ; the in- 

 florescence indefinite, and the evolution of the flower centripetal. The flowers at the lower 

 part of the spike have passed into fruit, those towards the middle are in full bloom, and 

 those at the top are only in bud. Fig. 259. Amentum or catkin of Hazel (Corylus Avdlama), 

 consisting of an axis or rachis covered with bracts in the form of scales (squatncB), each of 

 which covers a male flower, the stamens of which are seen projecting beyond the scale. The 

 catkin falls off in a mass, separating from the branch by an articulation. Fig. 260. Spadix 

 or succxilent spike of Arum maculatum. 1 Exhibits the sagittate leaf, the spathe or sheath- 

 ing bract, h, rolled round the spadix, the apex of which, a, is seen projecting. 2 Shows the 

 spathe, 6, cut longitudinally, so as to display the spadix, a. f, Female flowers at the base. 

 m, Male flowers. On the spadix above the male flowers there are mimerous abortive flowers 

 indicated by hair-like projections. 



