CH. xi] Double Flowers 197 



attained by an actual multiplication or division of the 

 petals, the stamens and other parts remaining apparently 

 unchanged. Of this some of the double Fuchsias, Hya- 

 cinths and several Liliaceae afford very clear examples. 

 These two processes, however, very often, in fact most 

 usually, occur in combination with each other, and it is not 

 generally possible to distinguish how much of the change in 

 number is due to the one process and how much to the 

 other. 



In some flowers, especially those with gamopetalous 

 corollas, the reduplication can occur in such a way that the 

 corolla is simply repeated, two or more corollas standing 

 in the place of one, but sometimes when two corollas 

 are thus formed it may be seen that the outermost is in 

 reality formed by a homoeotic variation of the sepals into 

 the likeness of the petals. The most familiar examples of 

 this " hose-in-hose " arrangement are known in Primula, 

 Campanula and Mimulus. Another kind of doubling is 

 due to what is termed proliferation or prolification (Masters) 

 of the floral envelopes. The best illustration of this is the 

 common double Arabis albida, in which the corolla and 

 calyx are repeated tier above tier on an elongation of the 

 axis. The different forms of increase in the number of 

 the petals may commonly occur in varying degrees of 

 perfection, and many grades of doubling are often to be 

 seen on the same individual plant. There is also evidence 

 that, in certain cases at least, high feeding and generous 

 cultivation greatly promote the doubling. In some forms 

 too it is known that the amount of doubling undergoes a 

 change with the age of the plant, showing what has been 

 called " Periodicity*," the most extensively doubled flowers 

 appearing on the strongest stems and at the height of the 

 flowering period. 



To students of genetics the interest of the doubling of 

 flowers arises partly from the fact that it is a character the 

 heredity of which can be readily investigated, but especially 

 from the obvious suggestion that the phenomenon is or at 

 least may be associated with disturbance in the sexuality of 

 the plants. 



* See Correns, JB. Wiss. Bot. XLI. 1905, p. 465, de Vries, Ber. 

 Deut. bot. Ges. xvu. 1899, p. 45.* 



