SOME OF THE PRINCIPLES OF PLANT- BREEDING 



59 



Fig. 80. Dwarf leafy sport or mutation 

 of com on left, which, when self-pol- 

 linated, reproduced original type. 

 Mother parental types on right. 



The third type of variation which is of impor- 

 tance to the plant -breeder is that produced by 

 hybridization or crossing, and here we probably 

 have the most prolific source of variations, and, 

 therefore, the class of variation of the greatest 

 importance and most consequence to the breeder. 

 It has come to be an established policy to combine 

 the good qualities of two races into a single race 

 by hybridization and selection. 



Influence of environment. — 

 It is a well-known fact that 

 environment has a decided in- 

 fluence on the form and char- 

 acter of the 

 plant. It is by 

 no means cer- 

 tain, however, 

 that these 

 changes are of 

 any value to 

 the plant- 

 breeder. It 

 seems certain 

 that those 

 changes which 

 are the conse- 

 quence of en- 

 vironmcnt 

 purely are not 

 hereditary. It 

 is a well-known fact that if climbing or twining 

 beans or viny cowpeas are transferred from a south- 

 ern to a northern climate or from a lower to a higher 

 altitude, they tend to produce a dwarfed type which 

 will not show the twining or viny habit in such 

 marked degree ; and in order to secure bush types 

 by selection, breeders have sometimes advocated 

 the transferring of types to more northern latitudes 

 or to higher altitudes, where the experiments may 

 be made under conditions that naturally lead to the 

 production of a lower bush type. It is doubtful, 

 however, whether such a transfer would be of 

 material aid. While it is recognized that such 

 variations are produced as an influence of the 

 environment, it is also known that, on the whole, 

 those variations which are produced as an immedi- 

 ate influence of the environment are not hereditary. 

 Individual variations and mutations are of greatest 

 use to the plant-breeder. Without question, if the 

 cowpea or bean were cultivated under southern 

 conditions it would show individual variations in 

 the degree in which it shows the climbing or twin- 

 ing habit. Even under southern conditions, certain 

 individuals would doubtless show more of the bush 

 type than others. It is believed by the writer that 

 a bush type can be secured just as quickly under 

 southern conditions by selecting from these lower 

 and more bushy plants as it can by the same 

 selection made in more northern localities or at 

 higher altitudes. 



Location of breeding plots. 



It is important to consider the conditions under 

 which the breeding patch or plat should be grown. 

 Some growers are inclined to locate their breeding 



patches in the garden and give the plants the very 

 best possible care, thinking that this is the best 

 means of determining which plants are superior. 

 Animal-breeders also isolate their breeding stocks 

 and give them every possible care and advantage. 

 On the contrary, some plant-breeders assert that 

 it is best to have the breeding patch located on 

 soils which are most like those on which the gen- 

 eral crop is to be grown. The writer has given 

 this matter considerable thought, and he is strongly 

 of the opinion that the most satisfactory method is 

 to cultivate the breeding patch under the same 

 conditions under which the ordinary crop is to be 

 grown; Plants are fixed in one place, and are 

 entirely dependent on the local soil conditions. If, 

 therefore, the plant has been bred and adapted to 

 one soil condition, it cannot be expected to give as 

 good results under different soil conditions. If a 

 variety is being bred for sterile soils, the selection 

 should be conducted on similarly sterile soil in 

 order to breed a race of individuals that are " gross 

 feeders," as planters term it, and capable of deriv- 

 ing their nutriment from sterile soils and making 

 a sturdy growth even under adverse conditions. 

 If, for example, plants were being bred to adapt 

 them to alkaline conditions, the breeding patch 

 should not be placed in a sheltered, favored spot, 

 wheYe the soil does not contain alkali. The plants 

 must be grown under alkaline conditions in order 

 to discover, as a result of natural selection, those 

 plants which do the best where the alkali is 

 present, and thus guide us in the selection. The 

 same would be true in breeding plants for arid 

 regions. The plants should be cultivated in the 

 arid region rather than in a moist region of heavy 

 rainfall, or in a thoroughly irrigated patch. 



In urging that the breeding patch be placed on 

 the ordinary soils and cultivated under the condi- 

 tions to which the crop is to be subjected, it is not 

 intended to convey the idea that the breeding 

 patch should not be given careful cultivation. 

 Slipshod methods of cultivation should never re- 

 ceive encouragement. The breeding patch should 

 be given thoroughly good cultivation ; and such 

 thoroughly good cultivation should also be used in 

 the field when the crop is grown on a more exten- 

 sive scale. 



Necessity of a clearly defined ideal. 



Careful breeders have found it very desirable 

 and necessary to have a clearly defined ideal type 

 which they are striving to produce. In the selec- 

 tions within the race it is necessary that the 

 breeder have clearly in mind all of the characters 

 of the race which he is breeding, and the writer 

 thinks that all breeders should be recommended 

 to draw up carefully a description of the type 

 which they are breeding and the objects which they 

 are attempting to obtain, otherwise it is difiicult 

 properly to limit the selections. All breeders know 

 that in growing a large number of plants for 

 selection, different types that appear very promis- 

 ing are likely to crop out here and there. We 

 may be selecting for a certain type, and find in the 

 row of plants which we are examining an individual 



