DOMESTICATED PLANTS — BLAYDES 323 



simple Mendelian ratio. If a pure white-grained plant is pollinated 

 with pollen from a hybrid individual, the ear developing on the whi^e 

 plant will show a 1 : 1 ratio of red to white grains and demonstrate the 

 "backcross" of the geneticists. Because of these heritable variations 

 and many others, corn, or maize, lias become one of the most important 

 tools in the study of heredity. 



Wheat {Triticum aestwu?7i) (pi. 4, fig. 19) is another grain of the 

 grass family, and has been in cultivation for at least 5,500 years. The 

 earliest remains were found in Mesopotamia. The grain is not as large 

 as the maize grain, but has a large endosperm with starch and protein 

 accumulated in it. The wheat seed is a basic source of food, serving 

 nearly half the human population of the world. In the United States 

 the wheat yield was 1,291,000,000 bushels in 1952. 



Some place in southeastern Asia, rice {Oryza satlva) (pi. 4, fig. 20) 

 became domesticated earlier than 2800 B. C. Over 5,000 varieties 

 have been recorded. The wild ancestor is unknown. The rice seed is 

 a basic source of food for nearly a billion people. 



MAN AND HIS DEPENDENCE UPON SEED PLANTS 



By the beginning of the great Ice Age, the Pleistocene period, 

 1,500,000 years ago, the world stage of vegetation became set in sucli 

 a way that our modern seed plants (angiosperms) were highly de- 

 veloped. A new actor began to make appearances on this stage — he 

 was known as man. He was able to survive because he could obtain 

 the right kind of food supply from the abundant flora, and materials 

 were available from which he could make clothing and construct 

 shelter, and which he could use as fuel for w^arnith and solace for his 

 ailments. He was a wanderer, endowed with intelligence far superior 

 to any other animal, and had inherited knowledge of how to survive 

 from his primate ancestors. It was essential for him to have intimate 

 knowledge of the plants which were useful to him as well as those 

 which were harmful — developing the rudiments of plant taxonomy. 

 He learned to make weapons in protecting himself from other animals, 

 and eventually to use these animals for food and their skins for 

 clothing. Some groups learned to live almost entirely by hunting, 

 making it necessary to follow the herds. Some were gatherers of food, 

 or perhaps combined the two methods of livelihood. They learned, 

 perhaps, to care for particular trees that bore desirable fruit. In dig- 

 ging for edible roots, bulbs, tubers, and rhizomes, they became aware 

 of vegetative propagation. 



Some of the more botanically minded noticed that some of the seeds 

 they ate had sprouts on them, and upon looking further saw various 

 seedlings develop to mature plants bearing the same kind of seed. 

 The discovery of these relatively simple processes and attendant re- 



