CONTENTS " xiii 



Page 

 and crossing-over — Assignment of linkage groups to chromosomes — Location 

 of genes in the chromosome — Chromatid exchange as the mechanism of 

 recombination — Mendelism in monoploid plants — The gene theory — 

 Summary. 



CHAPTER XVIII 



Fragmentation and Translocation 314 



Fragmentation of chromosomes — Behavior of free fragments — Inversion — 

 Translocation — Bearing on the chromosome map — Discussion. 



CHAPTER XIX 



Reciprocal Translocation 327 



Origin of the theory (Datura) — Reciprocal translocation in Zea — ffinothera. 



CHAPTER XX 



Heteroploidy 339 



Terminology — Heteroploidy in related species — Chromosome numbers in 

 related genera— Heteroploidy within species and individuals — How differ- 

 ences in number arise — Autoheteroploidy and alloheteroploidy. 



CHAPTER XXI 



The Cytogenetics of Autoheteroploid Plants 350 



Tetraploids and tetrasomics — Triploids and trisomies — Other heteroploids — 

 Monoploid sporophytes — Other features of autoheteroploids. 



CHAPTER XXII 



The Cytogenetics of Hybrids 359 



Diploid hybrids with good synapsis and fertility — Partial asynapsis and its 

 results — Synapsis in relation to polyploidy in hybrids — Analysis of allo- 

 heteroploid types — Amphidiploid hybrids — Parental characters in polyploid 

 hybrids — Segregation of parental chromosome sets — A fertile tetraploid 

 obtained through a sterile triploid — Conclusions. 



CHAPTER XXIII 



Chromosomes and Sex 375 



Sex-chromosomes in animals — Bryophytes — Algaj and Fungi — Angio- 

 sperms — Sex-linkage — Heteroploidy and sex — Modification of sex — Con- 

 clusion. 



CHAPTER XXIV 



Apomdcis and Related Phenomena 401 



Plants: Apomixis — Parthenogenesis — Apogamy — Sporophytic budding — 

 Apospory — False hybrids — Pseudogamy — Androgenesis — M e r o g o n y — 

 Causes of apomixis. Animals: Parthenogenesis — Parthenogamy — False 

 hybrids — Gynogenesis — Androgenesis — Merogony — Parthenogenesis and 

 heteroploidy. 



CHAPTER XXV 



Cytoplasmic Heredity 414 



Chlorophyll inheritance — Theories of chlorophyll inheritance — Mosses — 

 Other cases — Conclusions. 



