THE PRINCIPLE OF ARRANGEMENT. 47 



be more than one influence at work to determine what whorl 

 shall follow each of those of the perianth. 



The immediate cause is nutrition ; but the deeper question, 

 what dii'ects the nutrition to one cord rather than another, 

 can only be guessed at in most cases : but as the petaline 

 stamens are generally absent from at least the gamopetalai, 

 it would seem that the enhancement of the corolla through 

 the agency of insects has caused the whorl of stamens in 

 front of it to be atrophied through compensation. Some 

 special circumstance, however, we know not what, have 

 interfered to retain that whorl in Primulacece, and some few 

 other plants. 



The reader must be reminded, however, that this method 

 of branching in order to give rise to stamens and carpels 

 from the cords of the perianth is not universal. "When they 

 ai-e many, it is done by the fibro-vascular cylinder of the 

 pedicel becoming much enlarged, and consisting of a great 

 number of cords, all arising by lateral chorisis, it is true, 

 but long before they enter the floral members ; so that by 

 the time the latter are about to emerge they each receive 

 their own cords from the general axial cylinder. This is 

 what happens e.g., in Banunculacece and Cruciferce. 



