ANGIOSPERMS. 609 



the order in which the members of each whorl are themselves formed; -although the 

 two are in fact closely connected. A disturbance of the acropetal order of succession in 

 the formation of the whorls occurs when the carpels have begun to be formed before all 

 the stamens which stand below them have been produced, as in Rubus, Potentilla, and 

 Rosa\ or when the calyx is not formed until after the andrcecium (as in Hypericum 

 calycinum according to Hofmeister), or when the calyx is not observable until after 

 the corolla has become considerably developed or even after the formation of the 

 stamens and carpels, as in Compositae, Dipsacaceae, Valerianacese, and Rubiaceae. 



One of the most remarkable deviations from the general rule of the order of develop- 

 ment of the floral whorls occurs in Primulaceae, where five protuberances (primordia) 

 appear on the receptacle above the calyx, each of which grows up into a stamen, while 

 on the posterior or lower side of the base of each primordial stamen a lobe of the corolla 

 subsequently appears^. Pfeffer, who has observed this order of development (Jahrb. fiir 

 wissensch. Bot. vol. VII. p. 194), considers that the same probably also happens in the 

 pentandrous Hypericineae and in Plumbagineae ; he therefore explains the corolla- 

 lobes as posterior outgrowths of the stamens (a posterior ligular structure), such as, for 

 instance, occur on the stamens of Asclepiadeae in the form of hood-shaped nectaries, 

 where a true corolla is also present. The flowers of Primulaceae would therefore be 

 strictly apetalous in the morphological sense of the word, since their corolla is not a true 

 floral whorl, but only an outgrowth of the staminal whorl. In other families of Dicoty- 

 ledons, on the other hand, superposed corollas and androecia arise separately and in 

 acropetal order ; as, for instance, in Ampelideae, probably also in Rhamnaceae, Santalaceae, 

 and Chenopodiaceae. 



The individual members of a floral whorl may arise in succession from front to 

 back or the reverse, especially when the flowers themselves are subsequently developed 

 zygomorphically. Thus, for instance, in Papilionaceae the anterior median sepal is 

 formed first, then simultaneously one to the right and one to the left, and finally the 

 two posterior ones ; but before these last arise the two anterior petals appear, followed 

 by the two lateral and finally the posterior one ; and the andrcecium, consisting of two 

 alternating whorls of five stamens each, is formed in the same manner from front to 

 back\ In the Resedaceae, on the contrary {Reseda and Astrocarpus), Payer states that 

 the petals, stamens, and carpels are developed from behind forwards on both sides {cf. 

 Fig. 145, p. 187). 



When the calyx consists of pairs of sepals, those of each pair are formed, as Payer 

 has shown, simultaneously ; but if the calyx consists of three or five sepals, they are 

 usually formed one after another, and with the angle of divergence in the one case Ya? ^^ 

 the other ^5 ; but the succeeding whorls, the petals, stamens and carpels, usually arise 

 as simultaneous whorls, with the exceptions already named and others still to be 

 spoken of. 



It is well to draw attention here to the circumstance that it does not follow from the 

 order of succession advancing from one point, with a definite angle of divergence, say 

 Vs <^'' Vs) that the arrangement is a spiral one^; it may just as well in such cases be a 

 whorl. The nature of the arrangement depends on the circumstance whether the foliar 

 structures in question are formed at the same height or not, i, e. at an equal distance 

 from the centre of the flower ; if this is the case, we have a whorl ; but if the members 



^ Compare Hofmeister, Allgemeine Morphologic, pp. 463 et seq., where Payer's observations on 

 this point will also be found. 



^ [According to Frank (Ueb. d. Entwick. einig. Bluthen, mit bes. Beriicksichtigung der Theorie 

 der Interponirung, Jahrb. f. wiss. Bot. X. 1876), the stamens and petals of the Primulaceae arise 

 independently, but they fuse with the stamens during their development, and subsequently become free 

 again.] 



'■^ On the nearly related Coesalpinese see Rohrbach, Bot. Zeitg. 1870, p. 826. 



* Compare the successive true whorls of Chara and Salvinia, pp. 187, 191, 293, 449. 



R r 



