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 androecium (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 Compositse, Dipsacacea^, Valerianaceae, and Rubiaceae. 
One of the most remarkable deviations from the general rule of the order of develop- 
ment of the floral whorls occurs in Primulacese, 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'^. Pfeff"er, who has observed this order of development (Jahrb. für 
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 Ghenopodiaceae. 
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 Papiiionaceae 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 androecium, 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 consi-ts 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 Ys? 
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 or 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 Morphologie, pp. 463 el seq., where Payer's observations on 
this point will also be found. 
^ [According to Frank (Ueb. d. Entwick. einig. Blüthen, mit bes. Berücksichtigung 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 Csesalpinese see Rohrbach, Bot. Zeitg. 1870, p. 826. 
* Compare the successive true whorls of Chnra and Snlvinia, pp. 187, 191, 293, 449. 
R r 
