202 Plant-Breeding 



themselves unstable, when cross-fertilization is allowed 

 to take place, or when the pairs of contrasting characters 

 are very numerous and very complex. 



Application to plant-breeding. The wildest prophecies 

 have been made in respect to the application of Mendel's 

 law to the practice of plant-breeding, for the mathe- 

 matical formulae express only definiteness and precision. 

 Unfortunately, the formulae cannot express the indefinite- 

 ness and the unprecision which even Mendel found in his 

 work. The greatest benefit of Mendel's work to the 

 plant-breeder will be in improving the methods of ex- 

 perimenting. We can no longer be satisfied with mere 

 " trials'' in hybridizing: we must plan the work with 

 great care, have definite ideals, "work to a line," and 

 make accurate and statistical studies of the separate 

 marks or characters of plants. His work suggests what 

 we are to look for. 



The time may come when the hybridizer will be able 

 with many plants to make out beforehand plans and speci- 

 fications for their breeding and for carrying these through 

 with a large degree of exactness. 



The best breeders now breed to unit-characters, for this 

 is the significance of such expressions as "avoid breeding 

 for antagonistic characters," "breed for one thing at a 

 time," "know what you want," "have a definite ideal," 

 " keep the variety up to a standard." In certain classes 

 of plants the mendelian laws will be found to apply with 

 great regularity, and in these we shall be able to know be- 

 forehand about what to expect (Fig. 48) . The number of 

 cases in which the law or some modification of it applies 

 is being extended daily, both for animals and plants ; but 



