THE FLOWER 221 



of such flowers may be brought about by the transformation 

 of the disk-florets into florets similar to the ray-florets, which 

 often, however, is accompanied by a deficient development of 

 the sexual organs. Similar transformations take place in the 

 production of the double Guelder Eose ( Viburnum Opulus) and 

 in Hydrangea. In the latter case, it is, however, the calyx 

 which is the conspicuously developed portion of the flower. 



In the case of the capitulum of the Composites, the little 

 basket which encloses the flower, and which is often falsely 

 termed the calyx, is formed of a number of overlapping scales, 

 and should rightly be called the involuere. Besides these, a 

 number of bracts may be found between the several florets 

 and subtending them. Both these kinds of bracts may be 

 considerably enlarged and conspicuously coloured, and the 

 capitulum then has the appearance of a double flower. This 

 is the case with the " Everlasting Flowers " {Xeranthemwrn, 

 Helichryswin, Acrodinium roseum, and Bhodanthe Manglesii). 

 Such capitula very rarely divide, but occasionally small lateral 

 capitula make their appearance between the bracts of the 

 involucre. 



The tendency to " double " is always less in the case of 

 plants with a corolla in form of a single tube {gamopetcdous} 

 than when the corolla consists of a number of separate petals 

 {polypetalous) ; but among the latter there are some natural 

 orders which have no tendency to " double " ( Uitibelliferoe). 

 Speaking in general terms, we may say that it is easier to 

 produce double flowers in plants with radially symmetrical 

 than with bilaterally symmetrical flowers. 



Double varieties have, however, been produced in the case 

 of Viola, Pelargonium, Impaiiens, Pisum, Azalea, Lobelia, 

 Gloxinia, &c. 



§ 43. Can a gardener determine the development of flowers ? 



This question really resolves itself into two questions: — i. 

 Can a gardener cause the formation of new flowering buds ? 

 and, 2. Can he cause a change in the course of development 

 of existing floral rudiments ? In answering these questions. 



