244 Dr Dickson on I)i2jlosfemo7ious Flowers, dc. 



mens of inferior degree which may be superposed to the 

 petals. It appears to me that in Oistus and Capparis, all 

 the stamens superposed to the petals (including of course 

 the stamens of the second degree) must be looked upon 

 simply as neutral structures, resulting from the coalescence 

 of parts at the points of fusion of the contiguous groups, 

 just as "interpetiolar stipules" are neutral structures, re- 

 sulting from the coalescence of the stipules of opposite 

 leaves at the points of fusion of the leaf-bases. This 

 analogy will at once be admitted as a legitimate one, when it 

 is remembered that stipules are nothing but lobes of the leaf. 



To sum up, I think it is sufficiently evident from the 

 foregoing considerations, that all the instances of indefinite 

 stamens exhibiting an apparent deviation from the law of 

 centripetal succession of leaves upon an axis, may be re- 

 solved into cases of compound stamens with development 

 of lobes from above downwards. 



From this conclusion we are naturally led to inquire 

 whether those diplostemonous forms, where the younger 

 stamens are the more external, may not in like manner be 

 found to be merely apparent deviations from the ordinarily 

 recognised laws of leaf-succession ? We are at least bound 

 to show that the phenomenon is incapable of explanation 

 by the action of known laws, before we admit it to be an 

 example of centrifugal succession of leaves upon an axis.* 



In the Geraniacem^ which, as I have already mentioned, 

 exhibit this form of diplostemony, the genus Monsonia 

 presents the remarkable peculiarity of having ten stamens 

 in the younger and outer circle, arranged in five pairs 

 superposed to the petals.f Payer considered that these five 



* It may be observed that I bave bere left out of view tbe centrifugal evolu- 

 tion of ovules upon central placentas. I bave done so, because it is vain to 

 discuss this subject until we bave more definite notions tban at present pre- 

 vail on tbe morpbological value of tbe ovule itself. If tbe ovule represents a 

 modified leaf, the ovular groups will probably fall under tbe same category 

 with tbe staminal groups of polyadelphous plants, tbe placental elevations cor- 

 responding to tbe staminal bosses or cushions. If, on tbe other band, tbe 

 ovule is to be viewed as a bud or branch, analogies may be sought for among 

 contracted centrifugal inflorescences. 



t Similarly, in the Zygophyllacece, tbe five outer and younger stamens of 

 Zygophyllum, &c., are replaced in Peganum by five pairs of stamens superposed 

 to the petals. — Payer, Organogenie, p. 69 ; pi. 14, fig. 28. 



