422 



FOURTH GROUP. SEED-PLANTS. 



In cyclic flowers we must first of all distinguish between the succession of the whorls 

 among themselves and the formation of the members in each whorl, though the two are 

 in fact closely connected. A disturbance of the acropetal order in the development of 

 the whorls is observed, for example, when the carpels begin to form before all the 

 stamens beneath them have made their appearance, as happens in Rosa, Potentilla and 

 Riebus 1 , or when the calyx is formed after the androecium as in Hypericinn calycinitin 

 (Hofmeister), or when the calyx does not appear till after the development of the corolla 

 is considerably advanced or even till after the formation of the stamens and carpels, as 

 in the Compositae, Dipsaceae, Valerianeae, Rubiaceae. 



One of the most remarkable deviations from the general rule for the order of 

 development of the floral whorls occurs in the Primulaceae, where five primordia 

 appear on the torus above the calyx, each of which developes into a stamen ; subse- 

 quently a lobe of the corolla arises from the dorsal (under) side of the base of each 

 rudimentary stamen. Pfeffer, who observed this order of development 2 , considers these 

 corolla lobes as dorsal outgrowths of the stamens, dorsal ligular structures, such as are 

 found in the form of hood-like nectaries on the stamens of the Asclepiadeae where there 

 is a true corolla also. According to this view the flowers of the Primulaceae would be 

 morphologically apetalous, since the corolla is not a true floral whorl but only an cut- 

 growth from the staminal whorl. In other families of Dicotyledons superposed corollas 

 and androecia arise separate from one another and in acropetal succession, as in the 

 Ampelideae, and probably also in the Rhamneae, Santalaceae, Chenopodiaceae, and 

 other families. 



The separate members of a floral whorl, especially if the flowers afterwards become 

 zygomorphous, may follow one another as they form from front to back or in the reverse 



way ; thus for instance in Papilion- 

 aceae the anterior median sepal is 

 first formed, then one right and one 

 left of it simultaneously, and then 

 the two obliquely posterior ones ; 

 before these last appear, the two 

 obliquely anterior petals are formed 

 and after them the other three in the 

 same order as the corresponding 

 sepals ; the androecium, consisting 

 of five alternating whorls of five 



FIG 350. Development of the flower of Reseda odorata; to the left members each, JS formed in the 



a younger bud, to the right an older bud with the anterior sepals removed - _, . 



and the posterior retained; ss sepals, pp petals, st stamens already of Same Way, tn6 parts SUCCeCClmg 



some size behind, but not begun to be formed in front, c carpel. Qne ano tl le r from front tO back 3 . 



In Reseda and Astrocarpus, on the 



other hand, the petals, stamens and carpels begin to be formed from behind according 

 to Payer*, and advance right and left towards the front (Fig. 350). 



If the calyx consists of pairs of sepals, the sepals of each pair are formed, according 

 to Payer, simultaneously ; but if the calyx is a whorl of from three to five sepals, they are 

 formed as a rule successively with a ^ or % divergence ; the whorls that follow them, the 

 corolla, androecium and gynaceum, usually appear as simultaneous whorls, apart from the 

 exceptions that have been named above and will be named below. It should be remarked 

 here, that an order of formation advancing from a certain point with a definite diver- 

 gence of ^ or , for example, does not by itself prove that the arrangement is a spiral one 5 , 

 it may quite as well be a whorl ; the question depends on whether the foliar structures 



1 Hofmeister, Allgem. Morphol. p. 462, where Payer's observations on this point are also given. 



2 Jahrb. f. wiss. Bot. VII, p. 194. 



3 On the nearly related Cesalpinieae see Rohrbach in Bot. Ztg. 1870, p. 826. 

 * See also Goebel in Bot. Ztg. 1882. 



5 Compare the successive true whorls of the Characeae. 



