LUTHER BURBANK 



the exposure again and again, each time for only 

 the thousandth of a second, you will ultimately 

 pile up on the negative a succession of impres- 

 sions, each like all the rest, that result in the 

 production of a strong, sharp negative. 



But if in making the successive exposures, you 

 were to shift the position of the camera each time, 

 changing the scene, you would build up a negative 

 covered with faint images that overlap in such a 

 way as to make a blurred and unmeaning picture. 



And so it is with the plant. Each hour of its 

 life there come to it certain chemicals from the 

 soil, certain influences of heat and moisture 

 from the atmosphere, that are in effect vibrations 

 beating on its protoplasmic life-substance and 

 making infinitesimal but all-important changes in 

 its intimate structure. The amount of change 

 thus produced in a day or a year, or, under 

 natural conditions, perhaps in a century or in a 

 millennium, would be slight, for the lifetime of 

 races and plants is to be measured not in these 

 small units but in geological eras. 



Nevertheless the influence of a relatively brief 

 period must make an infinitesimal change, com- 

 parable to the thousandth-second exposure of the 

 negative. 



And when a plant remains century^ after 

 century in the same environment, receiving gen- 



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