HELIANTHUS ANNUUS. 169 



II. THE INFLORESCENCE. 



The head consists of a number of more or less modified 

 flowers borne on a common receptacle. The outer ones usually 

 have their corollas very prominent, and distinctly unlike the 

 corollas of the inner flowers. Observe: 



1. The involucre, consisting of green leaf -like organs or bracts 

 that enclose the base of the head. Observe : 



a. The number of cycles of bracts. 



b. The way in which they enclose young heads. 



2. The raj-flowers, the outer ring of flowers. Observe: 



a. The prominent yellow corolla, tubular at base and flat- 

 tened above. The notched tips of these corollas are 

 taken to indicate the number of petals that the united 

 structure represents. 



b. The carpel with prominent style and stigma, on whose 

 base (ovary) the epigynous corolla seems to be borne. 



c. The absence of stamens. 



3. The disk-lowers, those occupying the part of the recep- 

 tacle surrounded by the ray-flowers. Remove a few of 

 the flowers and observe: 



a. The distinctly tubular corolla with five-toothed rim 

 (see 2 a above), supported by 



b. The elongated ovary. Extended from the mouth of an 

 older corolla is 



c. The two-parted style and its stigmas. 



Open the corolla of a rather young disk-flower and observe: 



d. The stamens with their anthers joined, thus forming a 

 tube that adheres closely around the style (syngenesi- 

 ous). 



By studying young and old disk-flowers observe: 



e. How the style elongates, forcing its tip up through the 

 stamen-ring. 



Mount the stigmatic end of the style and observe: 

 /. The pollen-grains upon it. 



