THE INFLORESCENCE, AND THE FLOWER 



267 



parts, sometimes additional whorls that are added. All these methods 

 appear exemplified in the Rosaceae. The following diagrams may be 

 quoted as illustrating the pleiomeric variations within that family, though 

 without suggesting any actual line of Descent (Fig. 191). I n Sibbaldia, 

 the pentamerous flower has five stamens. Quillaija has two whorls of five 

 (diplostemonous), and this probably represents the fundamental type for the 

 Rosaceae, as it corresponds to that of related families with the formula (S P , 

 A 5+5- G 5)- But in the Rosaceae the matter does not stop there. Further steps 

 are taken till an indefinite number of stamens is arrived at. For instance, 



Z J£. 



Fig. 191. 



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 j : two at k. 

 (After Goebel.) 



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 have occurred, (i) fission, (ii) interpolation of individual stamens, and 

 (iii) interpolation 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 



