128 FLOWERS. 



145. Opposite and verticillate leaves, therefore, differ from alternate leaves 

 only in the spaces that separate them being reduced to nothing. 



VI. Flowers. 



146. Flowers consist of two principal parts, namely, Floral Envelopes 

 (149), and Sexes (VII.) 



147. Of these, the former constitute what is popularly considered the 

 flower ; although the latter are the only parts that are absolutely essential 

 to it. 



148. However different they may be in appearance from leaves, they are 

 all formed of those organs in a more or less modified state, and altered in 

 greater or less degree by mutual adhesion. 



149. The floral envelopes consist of two or more whorls of transformed 

 leaves ; of which part is calyx, its leaves being called sepals, and part 

 corolla, its leaves being called petals. 



150. The sexes are also transformed leaves (187). 



151. The calyx is always the outermost, the corolla is always the innei- 

 most whorls ; and if there is but one floral envelope, that one is calyx. 



152. Usually the calyx is green, and the corolla coloured and more 

 highly developed : but the reverse is frequently the case, as in Fuchsia, 

 Ribes sanguineum, &c. 



153. A flower being, then, an axis surrounded by leaves, it is in reality 

 a stunted branch ; that is, one the growth of which is checked, and its 

 power of elongation destroyed. 



154. That flowers are stunted branches is proved, first, by all their parts, 

 especially the most external, occasionally reverting to the state of ordinary 

 leaves ; secondly, by their parts being often transformed into each other ; 

 and, thirdly, by the whorls of flower-buds being dislocated and actually 

 converted into branches whenever any thing occurs to stimulate them 

 excessively. 



155. Their most essential distinctive character consists in the buds at 

 the axillse of their leaves being usually dormant, while those in the exilhe 

 of ordinary leaves are usually active. 



156. For this reason, while leaf-buds can be used for the purpose of pro- 

 pagation, flower-buds cannot usually be so employed. 



157. Being stunted branches, their position on the stem is the same as 

 that of developed branches. 



-158. And as there is in all plants a very great difference in the develope- 

 ment of leaf-buds, some growing readily into branches, others only unfold- 

 ing their leaves without elongating, and many remaining altogether dor- 

 mant, it follows that flower-buds may form upon plants of whatever age 

 and in whatever state. 



159. But to produce a general formation of flower-buds it is necessary 

 that there should be some general predisposing constitutional cause, inde- 

 pendent of accidental circumstances. 



160. This predisposing cause is the accumulation of sap and of secreted 

 matter. 



161. Therefore, whatever tends to retard the free flow of sap, and causes 

 it to accumulate, will cause the production of flower-buds or fertility. 



