28 THE STRUCTURE OF FLOWERS. 



type of the Onagracece and quinary of the Scrophularinece 

 respectively. 



Trimerous Whorls. — The number three is strongly 

 characteristic of Monocotyledons, and appears to be in this 

 class the immediate result of the J phyllotaxis. In Dicoty- 

 ledons, however, there are certain orders in which it prevails, 

 and it will be noticed that the number of parts in those 

 orders is generally much increased ; as in Magnoliacece* 

 AnonacecB, Berheris, Laurics Campliora, Rumex, etc. In some 

 the andrcecium and gynoecium are so increased in number 

 that they cease to be whorled, but have become spirally 

 arranged on a more or less elongated receptacle and are 

 represented by the fractions y^ or 2t-* 



It has been demonstrated above that a pentamerous 

 arrangement is undoubtedly due to the | phyllotaxis, each 

 whorl constituting a cycle ; but if the fraction be a higher 

 one, as y% or ^'^y, then the number of parts in a cycle are too 

 great to be compressed into a whorl. Nature appears then 

 to adopt another method. Falling back upon the law that 

 with these arrangements no part of the continuous spiral, of 

 sufficient length to constitute a complete circle when pro- 

 jected upon a plane, ever contains more or less than three 

 leaves (excepting the ^ type), the series is now broken up 

 into a succession of ternary whorls, the whole forming the 

 complete flower, and, being taken together, corresponds to 

 about or exactly one cycle of a high type. Thus Barberry 

 has 3 bracts, 3 -f 3 sepals, 3 + 3 petals, 3 -j- ^ stamens 

 and one carpel ; that is, seven whorls of threes or twenty-one 



* In Magnolia an individual complication is introduced, in that the 

 immense number of stamens and carpels is secured by doubling the 

 whole number attributable to the j% arrangement. Consequently, instead 

 of there being five and eight " secondary spirals," there are ten in one 

 direction and sixteen in the other. 



