494 . Mutations 



duced double varieties. One of them is 

 the Japanese marigold, others are the cari- 

 natum and the imbricatum species. Nearly 

 allied are quite a number of garden-plants with 

 double flower-heads, among which are the 

 double camomiles. 



My attention was first drawn to the structure 

 of the heads and especially to the number of the 

 ray-florets of the corn-marigold. The species 

 appertains to that group of composites which 

 have a head of small tubular florets surrounded 

 by a broad border of rays. These rays, when 

 counted, are observed to occur in definite num- 

 bers, which are connected with each other by a 

 formula, known as " the series " of Braun and 

 Schimper. In this formula, which commences 

 with 1 and 2, each number is equal to the sum 

 of the two foregoing figures. Thus 5, 8 and 13 

 are very frequent occurrences, and the following 

 number, 21, is a most general one for apparent- 

 ly full rays, such as in daisies, camomiles, A mica 

 and many other wild and cultivated species. 



These numbers are not at all constant. They 

 are only the averages, around which the real 

 numbers fluctuate. There may even be an over- 

 lapping of the extremes, since the fluctuation 

 around 13 may even go beyond 8 and 

 21, and so on. But such extremes are only 

 found in stray flowers, occurring on the same 



