54^ 



Reading-Course for Farmers. 



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1 



Fig. 3. — Oat plants grow- 

 ing side by sjde in same 

 field, showing difference 

 in size due to crowding. 



From what has been said above it will be seen 

 that fluctuating variations are of value mainly 

 in the production of improved strains of a race 

 which differ from the general characters of the 

 race only in such characteristics as high yield- 

 ing capacity, which is soon lost when the selec- 

 tion is discontinued. Mutations or sports on 

 the contrary are of value in the production of 

 distinctly new races and varieties which main- 

 tain their new characters without continued 

 selection as in the case of the Cupid sweet pea. 



Aside from the above types or variations we 

 have another type usually known as physio- 

 logical variation which is the direct reaction o^ 

 the plant to a certain environment. A simple 

 illustration of such a variation is the differ- 

 ence in size due to growth on sterile or rich soil 

 or to crowding in the field (fig. 3). We know 

 that if we transfer a pole bean to the north it 

 tends to produce a bush type, and if we transfer 

 a cow -pea to the north it tends to shorten up its 

 vine and assume a bush habit. An interesting 

 illustration of such modifications is shown in the 

 ordinary red cedar (Juniperus virginiana). In 

 the rich moist soils of Pennsylvania, Maryland 

 and Virginia, this tree forms a beautiful tall 

 columnar top with dense foliage (fig. 4a). On 

 the dry sterile limestone hills of Kansas, Ne- 

 braska and Kentucky and in the sandy soil of 

 Florida the same tree produces a spreading, 

 scraggly top of entirely different character 

 (fig. 4b), If we transplant one of these trees 

 while young from sterile, barren soil to moist, 

 rich lands it assumes the tall columnar habit 

 as a result of the environment. 



Plant breeders have ordinarily assumed that 

 such modifications, which are the result of en- 

 vironment (fig. 5a and b), are of great import- 

 ance to^ them. This matter, however, is in grave 

 doubt. The information at our .command in- 

 dicates that these characters, which are physio- 



