390 A TEXT-BOOK OF BOTANY. 



and the petals are convolute. Furthermore, in addition to the 

 principal types of estivation and vernation already given, there 

 are a number of special modifications of these, depending upon 

 the number and arrangement as well as direction of the over- 

 lapping parts of the flower- or leaf-bud. 



Coalescence and Adhesion. — Not only may the divisions of 

 the same circle or whorl of the flower be united, but even those 

 of different circles, and a number of terms are used to describe 

 these modifications. 



When the divisions of the same circle are united there is said 

 to be a COHESION or coalescence of the parts. When the divi- 

 sions of different circles are united, as of stamens with corolla, 

 the union is spoken of as adhesion or adnation, as in Convolvulus. 



Chorisis and Multiplication of Parts. — In contrast with the 

 reduction in number of parts of the flower due to union, there may 

 be an increase in the number of parts due to simple division or 

 splitting of the parts, and this is known as chorisis or deduplica- 

 tion. An illustration of this is furnished by the stamens of the 

 orange flower, where from a single initial stamen or primordium 

 a group of from 3 to ii stamens may be produced. In other cases 

 there may be a multiplication in the number of parts from the 

 beginning, each part arising independently on the torus, as in the 

 stamens of rose. This, of course, would not be termed chorisis, as 

 no splitting or branching takes place. 



Double Flowers. — In double flowers there is an increase 

 in the number of petals, which is considered to be due to the 

 methods of cultivation and the stimulus of an increased food- 

 supply. This results in several ways: (i) By transformation of 

 the sporophylls, more particularly the stamens, into petals; (2) 

 by division or chorisis of the stamens or carpels with subsequent 

 transformation into petals; (3) by division or branching of the 

 petals; and (4) by the production of new series of petals. The 

 extra petals in double carnations and double roses trace their 

 origin to the stamens, while in Fuchsia they are the result of 

 chorisis of the petals. 



In the snow-ball ( Viburnum Opulus) and hydrangea the essen- 

 tial elements have undergone a complete transformation, and the 

 flowers, while lar^e and showy, are sterile. In the white water lily 



