90 PRACTICAL BOTANY. 



with sessile flowers — namely, the spike, spadix, catkin, and 



liead. 



1. Clusters with Pedicelled Flowers. 



173. A raceme is that sort of flower-cluster in which 

 the flowers, arranged- along the main axis, and borne on 

 distinct, simple pedicels, are oldest at the base of the axis 

 and youngest at its top. (PI. II., 16.) 



A panicle is a compound raceme, in which the pedicels 

 branch in an irregular manner, to support flowers. (PI. 

 11,18.) 



Umbel is an inflorescence, in which the pedicels rise, 

 spreading apparently from the same point — that is, the 

 top of the main axis, to the same level, like the rays of an 

 umbrella, the outermost pedicels bearing the oldest, and 

 the inner the youngest flowers. The flower-stalks of this 

 sort of inflorescence are called rays. When the rays of 

 an umbel are each terminated by a flower, we have a sim- 

 ple umbel, but when they branch again to form secondary 

 umbels (umbellets), we have a compound umbel. Prim- 

 rose, Milkweed, Crantzia, etc., have simple umbels. (PL 

 II., 19.) Compound umbels are borne by most Umbel- 

 worts. (PI. II., 20.) 



A corymb is a flower-cluster in which the pedicels, 

 springing from different points of the main axis, rise to 

 the same level, or nearly so, thus forming a level-topped, 

 or else a slightly convex, inverted cone, the lowest pedi- 

 cels bearing the oldest flowers. (PI. II., 22.) It is nothing 

 but a modified raceme, a raceme with elongated pedicels. 



Thyrsus is a compact panicle of pyramidal or oblong 

 outline, as, for example, the flower-cluster of Horse-chest- 

 nut. 



