130 Retrograde Varieties 



variety are essentiall\^ different. The charac- 

 ter in question may be present in the given spe- 

 cies or it may be lacking, but present in the other 

 group. In the first case a variety can only be 

 formed by tlie loss of the character, in the sec- 

 ond case it arises by the addition of a new one. 



The first mode may be called a negative pro- 

 cess, while the second is then to be designated 

 as positive. And as it is more easy to lose what 

 one has than to obtain something new, negative 

 varieties are much more common than are posi- 

 tive ones. 



Let us now take an instance of a character 

 that is apt to vary in both ways, for this is ob- 

 viously the best way of making clear what is 

 meant by a negative and a positive change. 



In the family of the composites we find a 

 group of genera with two forms of florets on 

 each flower-head. The hermaphrodite ones are 

 tubular with 5, or rarely 4, equal teeth, and oc- 

 cupy the center of the head. These are often 

 called the flosculous florets or disk-florets. 

 Those of the circumference are ligulate and 

 ordinarily unisexual, without stamens. In many 

 cases they are sterile, having only an imperfect 

 ovary. They are large and brightly colored and 

 are generally designated as ray-florets. As in- 

 stances we may cite the camomile {Anfheniis 

 nobilis), the wild camomile {Matricaria Cham- 



