Production of Double Flowers 507 



even if the plants are very strong and healthy, 

 has no such effect. But even here it remains 

 doubtful whether it applies to the period before 

 or after the internal mutation. On the other 

 hand success is not at all to be relied upon, nor 

 is the work to be regarded as easy. The in- 

 stances of double flowers said to be obtainable 

 at will, are too rare in comparison with the 

 number of cases, where the first indication of 

 them was found accidentally. 



Leaving all these doubtful points, which will 

 have to be cleared up by further scientific in- 

 vestigation, the high degree of variability re- 

 quires further discussion. It may be considered 

 from three different points of view according 

 to the limit of the deviation from the average, 

 to the dependency on external conditions and to 

 periodicity. It seems best to take up the last 

 two points first. 



On a visit to a nursery at Erfurt I once in- 

 spected an experiment with a new double varie- 

 ty of the common blue-bottle or blue corn-flow- 

 er. The plants were dependent on the weather 

 to a high degree. Bad weather increased the 

 number of poorly filled flower-heads, while 

 warm and sunny days were productive of beau- 

 tiful double flowers. The heads that are borne 

 by strong branches have a greater tendency to 

 become double than those of the weaker ones, 



