THE FLORAL SHOOT. 427 



original structure which is the source of others. It merely refers 

 to a mode of inflorescence which we attempt to recognize, and 

 about which we group those forms which have a resemblance to 

 one another. There are many forms of flower clusters which 

 do not conform to any one of our recognized types, and are very 

 puzzling. The evolution of the flower clusters has been natural, 

 and we cannot make them all conform to an artificial classifica- 

 tion. These types are named merely as a matter of convenience 

 in the expression of our ideas. The types usually recognized 

 are as follows: 



819. The raceme. The flower-shoot is more or less elongated, 

 and the leaves are reduced to a minute size termed bracts, while 

 the flowers on lateral axes are solitary in the axils of the bracts. 

 The reduction in the size of the leaves and the somewhat limited 

 growth of the shoot in length, makes the flowers more prominent, 

 and brings them into closer relation than if they were formed in 

 the axils of the leaves on the ordinary foliage shoot. The choke 

 cherry, currant, pokeweed, sourwood, etc., are examples of a 

 raceme (fig. 569). In most plants with the raceme type, while 

 the inflorescence is indeterminate, and the uppermost flowers 

 (those toward the end of the main shoot) are younger, still the 

 period of flowering is somewhat restricted and the raceme stops 

 growing. In a few plants, however, as in the common "shep- 

 herd's purse," the raceme continues to grow throughout the 

 summer, so that the lower flowers may have ripened their seed 

 while the terminal portion of the raceme is still growing and 

 producing new flowers. Compound racemes are formed when 

 by branching of the flower-shoot there are several racemes in a 

 cluster, as in the false Solomon's seal (Smilacina racemosa). 



820. The panicle. The panicle is developed from the raceme 

 type by the branching of the lateral flower-axes forming a loose 

 open flower cluster, as in the oat. 



821. The thyrsus is a compact panicle of pyramidal form, as 

 in the lilac, horsechestnut, etc. 



822. The corymb. The corymb shows likewise an easy tran- 

 sition from the raceme type, by the shortening of the main axis 



