ttXHfPOttCUD PLOWS Its 



155 



but it would be just as arbitrary to say that the 

 sepals are missiug. 



174. Most persons are familiar with the flow- 

 ering-dogwood, the small twisted -grained tree which 

 hangs its pink -white 

 sprays against the 

 woodlands in early 

 spring. Fig. 154 will 

 identify it at once. 

 It appears to have 

 four great petals, and 

 a cluster of essential 

 organs in the center. 

 If one of these cen- 

 tral parts is exam- 

 ined, however, it is 

 seen to have a co- 

 rolla of its own, with 

 stamens and a pis- 

 til, and each pro- 

 duces a seed. The 

 great "flower," then, is a cluster of inconspicuous 

 flowers and a circle of petal -like bracts. These 

 encircling bracts, whether of the dogwood, hepat- 

 ica, or strawberry, constitute an involucre. This 

 involucre may reinforce either a single flower or a 

 flower-cluster. 



175. If the flower is borne upon the end of an 



Fig. 155. 

 Staminate catkin of paper birch. 



