Plants in Relation to Man 483 



survive in order to mature? 4. Do plants under cultivation have to 

 meet the same difficulties? 5. Show that wild plants when adapted 

 to their surroundings survive, and when not adapted, perish. 6. Give 

 a descriptive term to the thinning-out process found in nature; to 

 that performed by man. 



7. What is meant by the fitness of individual plants to survive? 



8. What are the four conditions upon which natural selection depends ? 



9. Distinguish between natural and artificial selection. 10. Upon 

 what condition does artificial selection depend? 11. Will all the 

 offspring of any parent plant be equally well adapted to their environ- 

 ment? Why? 12. Give some notable instances of artificial selection. 



13. Give a brief account of Luther Burbank's work in improving plants. 



14. How was the blue poppy originated ? 



III. POLLINATION AND SEED PRODUCTION 



230. How man promotes variation. We have considered 

 so far only the chance variations which plants may show and 

 which, when discovered, may be selected and encouraged to 

 propagate individuals that repeat and accentuate their peculiar 

 characteristics. There are, however, plants developed inde- 

 pendently of chance variations. These are the products of 

 man's purposeful interference with nature's course. How can 

 this be done ? The answer to this question may be found by a 

 study of nature's method of fertilizing plants, or what is known 

 as pollination. It is by man's control of pollination that new 

 varieties and species of plants are produced. 



How can man control the pollination or fertilization of plants ? 

 To understand this process it is necessary first of all to examine 

 the structure of the flower, and to learn the use or function of 

 its various parts and of the flower as a whole. 



231. The flower: the floral envelope. The brightly colored 

 parts of the flower, which are generally the most striking, 

 are called the petals (Fig. 149). The petals in their complete 

 formation constitute the corolla. The principal function of 

 the corolla seems to casual observation to be the attraction of 

 insects. 



Examine the circle of green leaves, called sepals, which com- 



