188 PRINCIPLES OF GAEDENING. [CH. VI. 



wiugs, giving a motion, assisting to effect the same 

 impoitaiit process. But tliey have a still more 

 essential office, for although they are absent from 

 some plants, yet, if removed from those possessing 

 them before imj)regnation is completed, the ferti- 

 lization never takes place. They, therefore, per- 

 form in such cases, an essential part in the vegetable 

 economy ; and that they do so is testified by all the 

 phenomena they exhibit. They turn to the sun 

 open only when he has a certain degree of poAver. 

 and close at the setting of that luminaiy ; their 

 secretions are usually more odorous, more saccha- 

 rine, and totally differing from those of the other 

 organs of plants ; and in the absence of light those 

 secretions are not formed. 



The corolla is not always short-Hved, for, although 

 in some, as the cistus, the petals which open Avith 

 the rising sim, strew the border as it departs ; so 

 some, far from being ephemeral, continue until the 

 fiiiit is perfected. The dm'ation of the petals, how- 

 ever, is intimately connected with the impregnation 

 of the seed, for in most flowers they fade soon after 

 this is completed; and double flowers, in which it 

 occm's not at all, ai*e always longer endming than 

 single flowers of the same species. Then, again, in 

 some flowers they become green, and perform the 

 functions of leaves after impregnation has been 

 effected. A familiar example occurs in the Christr 



