186 ECOLOGY 



167. Family Compositae. Most of the genera of this family found in 

 the United States are summer or autumn flowering. Two common genera 

 which flower in spring are Taraxacum and Erigeron. 



Taraxacum officinale, common dandelion. 



A. Sketch the entire plant. 



1. Notice the rosette formed by the leaves, all borne close to the 

 ground or even pulled below the surface by contraction of the tap 

 root. What is the use of this shortening of the tap root ? What 

 other plants show it ? 



2. Sketch the plant as seen from above. How much do the leaves 

 overlap and shade each other ? How much do they interfere with 

 the growth of grass in a lawn ? Advantages ? 



3. Taste the root and leaves. Use of this taste ? Are the leaves easily 

 injured by frost ? 



B. 1. Sketch the slender scape with its head of flowers. How do you 



know that the whole yellow " dandelion " is an inflorescence and 

 not a flower ? Advantage of grouping flowers in a head ? 



2. Changes in length of scape as it grows older ? Advantages ? 



3. Describe the involucre. 



4. What is its condition in the bud ? in a fully opened head ? in a 

 head that is past blooming ? in a head when the fruits ( "seeds " ) 

 are beginning to disperse ? 



5. Of what use is the involucre ? 



6. Make a longitudinal section through a newly blooming head and 

 note whether all the flowers mature together. 



7. The cushion-like expanded extremity of the scape, from which the 

 flowers spring, is a common receptacle for all the flowers of the head. 



C. 1. Note and describe the change in form of the corolla as the 



buds open. 



2. Decide from the number of teeth at the tip of the corolla and the 

 number of stamens what is the numerical plan of the flower. 



3. Slit open the corolla of a bud with a needle and scalpel, or two 

 needles, under the magnifying glass, and note the structure of the 

 flower. How many stamens are there ? From what part of the 

 flower do the filaments spring ? Are the anthers attached to each 

 other ? How do they open ? Position of the anthers relative to the 

 style *? How many branches has the stigma ? What is their form 

 and position (a) in the bud ? (6) in the newly opened flower ? 

 (c) in the flower just before withering ? What portion of the stigmas 

 is hairy ? 



4. When the stigmas emerge from among the anthers what do they 

 bring with them ? Importance of this ? Could the movements of 



