Plants in Relation to Man 495 



Many plants produce perfect flowers, which because of various 

 devices do not close-pollinate. 



Cross-pollination is effected by various agencies, such as wind 

 and insects. 



Wind-pollination is wasteful of pollen, as shown by corn. A 

 study of pollination by insects shows many mutually adaptive struc- 

 tures of flowers and insects. 



Flowers by their colors and odors attract insects to the nectar and 

 thereby secure cross-pollination. 



REVIEW QUESTIONS 



I. Of what practical importance is the control of pollination? 



2. What must we know about plants to control pollination? 



3. (a) What parts of the flower make up the floral envelope ? (6) What 

 advantage is it to a plant to have brightly colored flowers? 



4. (a) What are the essential or reproductive organs of a flower? 

 (6) Where is the pollen produced? (c) Where are the ovules formed? 



5. What do fertilized ovules become? 6. How is the stigma adapted 

 to hold the pollen grains that may touch it ? 7. Describe the growth 

 of the pollen tube. 8. What becomes of the two protoplasmic bodies 

 in the pollen tube? 9. What two parts of the seed develop from the 

 two parts of the generative cell? 10. How can you demonstrate the 

 value of the food supply to the growing embryo ? 



II. What is the significance of the term staminate flower? Pistil- 

 late flower? 12. (a) Mention a species in which staminate flowers 

 and pistillate flowers occur on the same individual plant. (6) In 

 what species do staminate and pistillate flowers occur on different 

 individual plants? 13. Describe the structure of the reproductive 

 organs, and the reproductive process of corn. 14. Mention a garden 

 plant that is self- or close-pollinated ; a wild flower. 15. Which is 

 the prevailing type, cross-pollinated or self -pollinated plants? 

 16. Mention several plants that depend upon wind for the transfer 

 of their pollen. 17. How are the following plants adapted to wind- 

 pollination: (a) corn, (6) willow, (c) timothy? 18. What are some 

 of the disadvantages of dependence on wind for pollination? 



19. Mention an instance of mutual adaptation of insect and plant. 

 20. Why do insects visit flowers? 21. By what means do flowers 

 advertise their presence to insects? 22. By what insect is red clover 

 pollinated ? 23. (a) What insects are adapted to reach the nectar in 

 long tubes? (6) In night-blooming flowers? 24. What flowers 

 depend mostly on their odor for attracting insects? 25. Why is the 



