THE INFLORESCENCE, AND THE FLOWER 233 



is arrived at For instance, in Agrimonia odorata there is an outer whorl of 

 five and an inner of ten (II.). In Potentilla there may be two whorls 

 of ten stamens each (III.) ; in Mespilus there may be four whorls of ten 

 each ; while in Rubus (IV.), taking account only of the two outermost 

 whorls, that next to the pentamerous corolla consists of ten stamens, but it 

 is followed by numerous stamens disposed in irregular groups varying from 

 one to four ; those groups alternate with the stamens of the outer whorl. 

 This points to an irregular interpolation of extra stamens. Such comparisons 

 suggest that in the Rosaceae three sources of pleiomery of stamens ihave 



FIG. 182. 



Floral diagrams of various Rosaceae (carpels omitted). I. Sibbaldia cuneata, 

 and some species of Agrimonia. II. Agrimonia odorata : the first whorl of five 

 stamens is followed by one of ten. III. Potentilla : the pentamerous corolla is 

 succeeded by a whorl of ten stamens, alternating with ten stamens of the second 

 whorl. IV. Rubus idaeus (special case. The pentamerous corolla is followed by a 

 whorl of ten stamens, and from one to four stamens according to the growth of 

 the zone of the floral axis are interpolated in the Intervals between each pair of the 

 first stamens, not only one as in III. There are three at a : one at b : three at c : 

 two at d : two at e : two at / : four at g : two at h : three at t : two at k. 

 (After Goebel.) 



occurred, (i) fission, (ii) interpolation of individual stamens, and (iii) inter- 

 polation of extra whorls of stamens. 



The diplostemonous state, where the stamens are twice as many as the 

 petals, is common in those Dicotyledons and Monocotyledons which have 

 cyclic flowers. Many polypetalous Dicotyledons show it, but with slight 

 modification of position of the stamens, which suggest that it may have 

 originated in different ways. It is represented also in the Gamopetalous 

 Dicotyledons, which are divided into Tetracyclicae which have only one 

 whorl of stamens, and Pentacyclicae which have two ; making in all five 

 cycles of floral parts. The Pentacyclic type is prevalent also in the 

 Monocotyledons, as shown by the Liliaceous type of flower, with its many 

 derivatives. The biological meaning of such facts is to be found in 



