316 APPLICATION OP PRINCIPLES. 



exchanged for petals, or in which the number of the 

 latter is augmented without any disturbance of the 

 former; in other words, it is a case of the loss, on the 

 part of a plant, of the power necessary to develope its 

 leaves in the state of sexual organs (83, 84). But 

 what causes .that loss of power we do not know. It 

 can hardly be a want of sufficient food in the soil; 

 for double flowers (the Narcissus, for instance) be- 

 come single in very poor soil. On the other hand, it 

 can scarcely be excessive vigour ; for no one has ever 

 yet obtained a double flower by promoting the health 

 or energy of a species. When plants are excessively 

 stimulated by unusually warm damp weather at the 

 period of flowering, their flowers in such cases some- 

 times became monstrous : but the effect of this is to 

 lengthen their axis of growth, and to form true leaves 

 instead of floral organs (84, fig. 14), just the reverse 

 of what occurs in a truly double flower; the varieties 

 of Rosa gallica often exhibit this kind of change. En 

 damp cloudy: summers, some 'flowers assume the ap- 

 pearance of being double, by the change of their 

 sexual organs into small green leaves, as occurred 

 very generally to Potentilla nepalensis in the summer 

 of 1839, a representation of which is given at page 

 61 ; but there was, at the same time,- scarcely a trace 

 of any tendency, on the part of those leaves, to assume 

 the colour or texture of petals. 



There is, evidently, a greater tendency in some 

 flowers to become double than in others, and especial- 

 ly in those having great nunjbers of stamens or pistils. 

 All our favourite double flowers, Hepaticas, Pseonies, 



