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CYTOGENETICS AND EVOLUTION 

 OF THE GRASS FAMILY 



G. Ledyard Stebbins 



During the past half century that part of botany, and in fact all biological 

 science, which deals with evolution and classification has entered a new era, 

 dominated by the rise of cytology and genetics and their use as new tools for 

 solving evolutionary and taxonomic problems. This union of disciplines has 

 yielded striking results, and the new relationships uncovered by it have often 

 been supported by data from still other fields, such as anatomy, embryology, 

 and physiology. Thus plant evolutionists are gradually progressing toward 

 their avowed goal: the understanding of the complex interrelationships be- 

 tween and the evolutionary origin of the myriad diverse t5T3es of plants 

 existing on the earth and the establishment of general principles which have 

 governed this evolution. 



No group of plants has been more radically affected by this new ap- 

 proach than the grass family. There are several reasons for this. In the first 

 place, grasses are very important to us. They feed our cattle, sheep, and 

 other livestock. A few species of the family, the cereal grains, have become our 

 staple foods, while another, sugar cane, sweetens our lives. If we are home 

 owners, we cut the grass every week so that we can enjoy the soft turf and 

 cool green expanse of our lawns; and while resting we often pluck its leaves 

 or stems, admire their structure, or teach our youngsters how to turn a grass 

 leaf into a shrill whistle by placing it between our thumbs. If we live in a 

 dry climate and hike over the hills in summer, we come home to spend hours 

 plucking the seeds of the weedy or "stickery" grasses out of our clothing 

 or our dog's hair. In many parts of the world one group of grasses, the bam- 

 boos, are the staple building material for houses and bridges. 



Because of these many uses, the study of grass classification, or taxonomy, 

 does more than satisfy our curiosity about the diversity of living things and 

 the way in which they have evolved. Cereal and sugar-cane breeders have 

 learned that many species of wild grasses are closely enough related to the 



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