244 



CYTOLOGY 



have been lost. Those of us who are 

 famihar with the cytological facts and 

 have speculated about their overall 

 meaning, have suggested that hybridi- 

 zation was probably just as common 

 among the diploids and may well have 

 involved rare crosses with other genera. 

 Such h\potheses can be proved for 

 diploid crops but it takes much more 

 time and requires more elaborate re- 

 search programs. 



In the second place the cvtological 

 evidence demonstrates the intimate 

 connection between crop plants and 

 weeds. Einkorn, our most primitive 

 wheat, was essentiallv built up into a 

 world crop by hybridizations with its 



own weeds, Aegilops, Agropyron, and 

 llaynaldia. 



Most important of all, the cvtol- 

 ogical evidence demonstrates that the 

 histor)' of any major crop is a long in- 

 volved affair. Tliere was a time when 

 anyone with a good general background 

 in biology could look up the scientific 

 names of our major crop plants (if he 

 did not already know them), ascertain 

 what parts of the world they were said 

 to come from, and write a definitive 

 article concerning the origin of agri- 

 culture. That time is past. One of the 

 chief services of the new evidence from 

 cytology and genetics has been to show 

 up the experts. 



QUESTIONS 



Explain how cytologists can tell us 

 something about the ( 1 ) origin of a 

 plant, (2) its relationship to other 

 plants. 



Describe brieflv the origin of culti- 

 vated wheat. 



How is colchicine valuable to the plant 

 breeder? 



4. How does hybridization speed up evo- 

 lution? 



