Laivs of Fluctuatioyis 719 



the whole method of statistical investigation. 

 It is equally important for the discussion of the 

 contrast between fluctuations and mutations, 

 and for the appreciation of their part in the 

 general progress of organization. Mutations 

 are going on in all directions, producing, if they 

 are progressive, something quite new every 

 time. Fluctuations are limited to increase and 

 decrease of what is already available. They 

 may produce plants with higher stems, more 

 petals in the flowers, larger and more palatable 

 fruits, but obviously the first petal and the first 

 berry cannot have originated by the simple in- 

 crease of some older quality. Intermediates 

 may be found, and they may mark the limit, but 

 the demonstration of the absence of a limit is 

 quite another question. It would require the 

 two extremes to be shown to belong to one unit, 

 complying with the simple law of Quetelet. 



Nourishment is the potent factor of fluctuat- 

 ing variability. Of course in thousands of cases 

 our knowledge is not sufficient to allow us to ana- 

 lyze this relation, and a number of phases of the 

 phenomenon have been discovered only quite 

 recently. But the fact itself is thoroughly mani- 

 fest, and its appreciation is as old as horticul- 

 tural science. Knight, who lived at the begin- 

 ning of the last century, has laid great stress 

 upon it, and it has since influenced practice in a 



