210 



BOTANY: PRINCIPLES AND PROBLEMS 



in our knowledge, and we are now beginning to see that there are 

 indeed laws of inheritance, an understanding of which will enable 

 us to raise the art of breeding from clever but uncertain guess- 

 work to such a firm scientific basis as that upon which chemistry 

 and physics now rest. An investigation of these laws is the 

 province of the modern science of genetics. 



Inheritance of Acquired Characters.— We have learned, for 

 example, that all variations do not behave alike in inheritance. 

 Some are due to factors embodied in the constitution of the 



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Fig. 121. — Variation produced by the environment. A, Plant of the dandelion 

 (Taraxacum) grown in a lowland garden. B, Portion of the same plant grown in 

 an alpine garden, under relatively unfavorable conditions. (From Bonnier). 



gametes and may thus be transmitted from one generation to the 

 next. They are clearly inheritable and are the "raw material" 

 with which the breeder may work. Other variations, and among 

 them many important ones, result from the direct action of the 

 environment upon the plant body during its growth and are 

 apparently never transmitted to offspring. Such "acquired" 

 characters are the increased size and vigor which result from 

 growth in rich soil (Fig. 121), the thick and heavy leaves developed 

 by many plants when exposed to bright sunlight, the galls and 

 other malformations resulting from insect or fungus attack, the 

 stunting effect of overcrowding, and many others. These varia- 



