1 6 THE CEREALS IN AMERICA 



ciples of breeding to plants, although they have been applied to 

 the breeding of animals for many years. Among the circum- 

 stances are the following : 



1. Lack of knowledge of the sexuality of plants until recent 

 times. 



2. Difficulty of control in breeding plants. 



3. The selection is made from seeds which are embryos and 

 not mature individuals. 



The last two circumstances apply much more to some plants 

 than to others. They apply with special force to ordinary field 

 crops. 



33. Sex. — The sexes in animals must have been known from 

 the earliest times. Camerarius first published experimental 

 proof of the sexuality of plants December 28, 1691. It was 

 not until after this discovery that the function of pollen and its 

 necessity to seed formation was understood. It \vill be readily 

 appreciated that this knowledge did not become general among 

 the growers of the staple crops until much more recent times 

 and is perhaps still not understood by many. Thus there has 

 been more or less systematic breeding of animals for 4000 

 years, while the mating of plants has not been practiced for 

 more than two hundred years. 



34. The Difficulty of Control in Breeding Plants. — The pollen 

 of plants cannot ordinarily be confined, while the male domestic 

 animal can be tied up by a halter or confined in a yard. In 

 some plants like maize w^hich is wind-fertilized we have no knowl- 

 edge of the plant from which the pollen came and consequently 

 no knowledge of the characteristics of the sire. In other plants 

 like wheat that are self-fertilized two individuals cannot be 

 mated without resorting to artificial means. 



35. The Seed an Embryo. — The selection is usually made 

 from the seeds. The seed is an embryo, not a mature indi- 

 vidual. The characteristics of the mature chicken cannot be 

 fully foretold by looking at the egg. The seed must be grown 



