GROWTH AND WORK OF PLANTS 



ing secondary corymbs, as in the mountain ash. It is like a 



panicle with the lower stalks elongated. 



5. The umbel. The umbel is developed from the raceme, or 



corymb. The main flower shoot remains very short or undevel- 

 oped with several flowers on long peduncles arising 

 close together around this shortened axis, in the 

 form of a whorl or cluster. Examples are found 

 in the milkweed (fig. 107), water pennywort 

 (Hydrocotyle), the oxheart cherry, etc. A com- 

 pound umbel is one in which the peduncles are 

 branched, forming secondary umbels, as in the 

 caraway, parsnip, carrot, etc. 



6. The spike. In the spike the main axis is 

 long, and the solitary flowers in the axils of the 

 bracts are usually sessile, and often very much 

 crowded. The plantain (fig. 108), mullein, etc., 

 are examples. The spike is a raceme, only the 

 flowers are sessile and crowded. In the grasses the 

 flower cluster is branched, and the branchlets bear- 

 ing a few flowers are spikelets. 



7. The head. When the flower axis is very 

 much shortened and the flowers crowded and 

 sessile or nearly so, forming a globose or com- 

 pressed cluster, it is a head. The transition is 

 from a spike by the shortening of the main axis, as 

 in the clover, button bush (Cephalanthus}, etc., or 

 in the shortening of the peduncles in an umbel, 

 as in the daisy (fig. 109), dandelion and other com- 

 posite flowers. In these the head is surrounded by 



an involucre, which in the young head often envelops the mass 

 of flowers, thus affording them protection. 



8. The spadix. When the main axis of the flower cluster is 

 fleshy, the spike or head forms a spadix, as in the Indian turnip 

 (% I 33)> the shunk cabbage, the calla, etc. The spadix is 

 usually more or less enclosed in a spathe, a somewhat strap- 

 shaped leaf. 



Fig. 108. 

 A spike (plan- 

 tain, one-half 

 real length). 



