228 BOTANY: PRINCIPLES AND PROBLEMS 



597. White disc crossed with white sphere gives three-eighths white 

 disc, three-eighths white sphere, one-eighth yellow disc and one-eighth 

 yellow sphere. 



598. Yellow disc crossed with white sphere gives all white discs. 



599. White disc crossed with white disc gives 28 white disc plants, 9 

 white sphere plants, 10 yellow disc plants, and 3 yellow sphere plants. 



600. A cross between a plant with white disc fruits and one with 

 yellow sphere fruits gives 25 plants with white disc fruits, 26 with white 

 sphere, 24 with yellow disc, and 25 with yellow sphere. If the white disc 

 parent is self-fertilized, what proportion of its offspring will have 

 yellow sphere fruits? 



601. Explain how it can be that plants which look exactly alike may 

 breed very differently. 



602. Hybrid animals and plants notoriously fail to breed true. Why? 



603. If a potato breeder desires to obtain a new variety of potatoes 

 by selection from among a large number of plants, would you advise 

 him to plant potato "seed" (pieces of the tuber) or real seed from the 

 seed capsule, to provide plants from which be may select? Why? 



604. Do you think that the characteristics of the fruits of an apple 

 tree will be affected by the kind of pollen which fertilized the flowers? 

 Explain. 



REFERENCE PROBLEMS 



96. Summarize briefly the hfe and work of Mendel and tell how his 

 discoveries were finally brought to the attention of the world. 



97. Give examples (aside from those mentioned in the text) of new plant 

 varieties which have arisen as a result of hybridization; as a result of 

 mutation. 



98. State briefly why it is that the chromosomes, rather than any other 

 part of the gametes, are believed to carry the hereditary factors. 



99. What is a "Pure Line" of plants? Of what importance are Pure 

 Lines in agricultural practice? 



100. What is meant by "bud selection" in horticultural practice? 



101. Give the derivation of the following terms and explain in what way 

 each is appropriate: 



Heredity Segregation Mutation 



Allelomorph Homozygous Genotype 



