THEORY AND PRACTICE 



day specimens are but dwarfed and insignificant 

 replicas. 



Similarly the double flowers that form so at- 

 tractive a feature in our gardens roses, dahlias, 

 marigolds, and the rest are probably reminis- 

 cent of clustered flowers of the antique world. 

 What is now the composite head of a single dahlia 

 or marigold or daisy was probably, in its pri- 

 mordial state, a cluster of flowers. Through nat- 

 ural selection such a cluster made an experiment 

 in communism, in which finally hundreds of flow- 

 ers were grouped, with a single circle of florets 

 to advertise their location to the insects. This 

 represented great economy, and the plan became 

 enormously popular, so that the composites are 

 among the most abundant of flowers. But each 

 individual blossom in a composite flower head car- 

 ries in its germ-plasm the factors for the develop- 

 ment of an independent corolla, and under favor- 

 ing conditions through hybridization or through 

 changed environment this potentiality is realized 

 in the production of what we term a double flower. 



In this way only can we explain such a phe- 

 nomenon as the rapid production of races of 

 double dahlias in the relatively short period since 

 the single dahlia was brought from Mexico and 

 given a place in the cultivated flower garden. 



[169] 



