PLANT BREEDING 115 



167. The breeding of plants is an application of the 

 principles of reproduction and heredity to the production 

 of plants with certain desirable characteristics. In- 

 stead of waiting for the chance production of a desirable 

 type of plant, the plant breeder either grows many plants 

 in conditions under his control and selects for further 

 propagation those he deems most desirable (method of 

 selection), or he takes two distinct plants, each with 

 certain characters that he desires, and crosses them, and 

 grows the progeny in large numbers for several generations 

 until by the laws of chance in the distribution of the 

 unit character determinants there appears a plant 

 combining the desirable characters of the two parents. 

 This is the method of hybridization or crossing. The 

 discovery by Mendel of the segregation of characters by 

 definite laws of numbers (see paragraph 165) has given a 

 great impetus to this line of work. 



Laboratory Studies. Not much can be done in the way of 

 laboratory work on this subject. In the study of the different 

 forms of plants in the later chapters of the book, the points 

 emphasized in the foregoing paragraphs should be borne in 

 mind. A few suggestions are made for observations on the 

 part of the student. 



(a) Find and compare carefully a dozen different plants of 

 timothy (Phleum pratense), red clover (Trifolium pratense), 

 ribbed plantain (Plantago lanceolata), etc. Select those 

 plants of the same age and from as nearly as possible the same 

 soil and growing under the same environmental conditions. 

 Note how they differ in height ; number, size and shape of leaves; 

 size of flower heads; number of flowers in the head; amount of 

 hairiness of various parts, etc. 



(b) Compare plants of the same kind grown in sun and shade, 

 in dry and moist soils, in barren and on fertile ground, for 

 differences due largely to the environment. Note the differ- 

 ences in the times of flowering and of ripening of seeds, as well 

 as the structural differences. 



