FLOWER-GARDENING. 139 



acid, and called into action only when the leaves are freely 

 exposed to light and air (279), it also follows that the quan- 

 tity of secretion will be in direct proportion to the quantity of 

 leaves, and to their free exposure to light and air. 



142. The usual position of leaves is spiral, at regularly in- 

 creasing or diminishing distances ; they are then said to be 

 alternate. 



143. But if the space, or the axis, that separates two leaves 

 is reduced to nothing at alternate intervals, they become 

 opposite. 



144. And if the spaces that separate several leaves be re- 

 duced to nothing, they become verticillate. 



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 con- 

 sidered 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 innermost whorls ; and if there is but one floral envelope, 

 that one is calyx. 



152. Usually the calyx is green, and the corolla colored and 



