THE FLOWER 211 



contain pistils, but no stamens ; they are, therefore, not petals, 

 but the corollas of imperfect flowers. Look at the upper edge 

 of a ray of sneezeweed, coreopsis, arnica, chicory, etc., for 

 small teeth or notches ; these represent the lobes of a sympet- 

 alous corolla. Split one of the tubular corollas of the disk 

 down one side and open it out flat ; does it throw any light 

 on the morphology of the ray ? In many composite plants, 

 as the sunflower, coneflower, coreopsis, the rays are all neutral; 

 that is, they have neither pistil nor stamens. Are they of any 

 use in such cases ? If you are in doubt, remove all the rays 

 from a head ; would the disk be noticeable enough to attract 

 attention without them? What is the principal office of 

 the rays? 



232. The involucre. — Look at the cluster of green, leafy 

 scales on the under side of the head. It is not a calyx, but 

 a collection of bracts, called an involucre. Have you ever 

 noticed the bracts under the separate flowers on a raceme? 

 (16L) What would be the position of the bracts if all the 

 flowers of the raceme were compacted into a head like the 

 daisy or sunflower? Is the involucre of any use? Cut it 

 away gently so as not to disturb the other organs and see 

 what happens to the rays. 



233. The disk flowers. — Cut a vertical section through 

 the head of a flower and notice the broad, flat receptacle (in 

 some cases round or columnar) on which the tinj^ florets 

 are seated. Observe whether it is naked, or whether it 

 bears chaffy scales inclosing the florets. Make an enlarged 

 drawing of this section, showing the insertion of the dif- 

 ferent parts and labeling them all correctly. What differ- 

 ences do you observe between the disk and the ray flowers ? 



234. The pappus. — ^ Open one of the disk flowers with a 

 dissecting needle and observe the small striate (in some 

 specimens, hairy) body to which the base of the style is at- 

 tached. This is the ovary, inclosed in the lower part of the 

 calyx, which has become incorporated with it. "When mature, 

 it will form a small, one-seeded fruit called an akene. Can 



