THE SHASTA DAISY 313 



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 nega- 

 tive covered with faint images that overlap in 

 such a way as to make a blurred and unmean- 

 ing 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 cen- 

 tury in the same environment, receiving genera- 

 tion after generation the same influences from 

 the soil and atmosphere, the stamp of these in- 

 fluences on its organic structure becomes more 

 and more fixed and the hereditary influence 



