TYPE STUDIES, SEED PLANTS 187 



the stigmas cause self-pollination ? At what period in their devolo].- 

 ment ? Advantages of this ? 



5. Look for nectar. How high does it rise in the corolla tube ? Acces- 

 sibility to small insects ? 



6. How many kinds of insect visitors do you find ? i 



7. Is the head open on sunny and cloudy days alike ? Is it open all 

 night ? Advantages ? Mark a head by tying twine loosely about the 

 scape and note how long it remains in blossom, how long it remains 

 closed after blossoming, and how long after reopening the last fruits 

 are dispersed. 



D. Sketch a fruit somewhat magnified and label the parts. Test the 

 traveling powers of some akenes in a gentle breeze. 



E. Study the distribution of dandelion plants in your neighborhood, state 

 where they thrive best, and give reasons. 



F. Write a brief essay on the ecology of the dandelion, discussing : 



(1) Relations to other plants. 



(2) Relations to leaf-eating insects and grazing animals. 



(3) Relations to pollinating insects. 



(4) Relations to weather. 



(5) Distribution of seed. 



Erigeron philadelphicus, common fleabane (or other species). 



A. Study the fully opened heads and make out a list of resemblances 

 to and differences from the head of the dandelion. Note that every 

 flower in the dandelion head has a strap-shaped corolla, and is bisexual. 



1. Where are strap-shaped flowers of the fleabane ? Are they bisexual? 



2. Sketch under the lens a tubular flower. 



B. Look for insect visitors. 



C. Discuss the relative equipment of the dandelion and the fleabane for 

 success in life. 



The family ComposltcB is the largest family of seed plants, comprising 

 about eleven thousand species. It is usually considered to be the highest 

 family. Not many Conipositce in temperate climates are shrubby or tree^ 

 like, but as herbs they show the greatest diversity of form and ecological 

 characteristics. As a rule, they are extremely successful in maturing and 

 distributing seed, and for this and other reasons constitute very formi- 

 dable weeds. 



Make a list of some of the commonest weeds of this family in your 

 neighborhood. 



References. Principles, Chapters XXXII, XXXIII ; Strasburger, Noll, 

 Schenck, Karsten, 1 ; Warming-Mobius, 37 ; Engler, 30 ; Knuth- 

 Davis, 62 ; Kerner-Oliver, 2. 



1 Nearly a hundred species have been noted in a single locality. 



