532 



PHANEROGAMS, 



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 Ampelidese, probably also in Rhamnacese, 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 androecium, consisting of two 

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

 backi. 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- 137, p. t66). 



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 one case Vs in 

 the other %; 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 75, 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, /. e. at an equal distance 

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

 arise in acropetal order at different heights, i.e. approaching the centre of the flower 

 with each step in the divergence, the arrangement is a spiral one. I'he last appears to 

 be actually the case in many calyces ; but it is doubtful whether it ever occurs where the 

 angle of divergence of the sepals is V3 oi" " 5- 



We must now refer again to the cases already mentioned, where new members of a 

 whorl are formed between those already in existence and at the same heights In the 

 Oxalidcce, Geraniaceae, Rutaceae, and Zygophyllaceae, an entire w-horl of five stamens is 

 thus interposed between those already present ; according to Payer, in Peganum Harmala^ 

 a whorl of ten stamens is even formed in this manner, arising, not in pairs between the 

 first five, but lower down at the bases of the petals ; whether the later formed stamens 

 arise on the same level with the first or lower down is obviously regulated according to 

 the space aff'orded by the changes of form of the growing receptacle. A still further 

 departure from the ordinary process occurs in the Acerineae, Hippocastaneae, and Sapin- 

 daceae, where Payer asserts that a whorl of five stamens is first of all formed alternating 

 with the corolla, in which an imperfect whorl of tw'o or four stamens is subsequently 

 interposed at the same height, as is shown by his illustrations. In Tropaeolum, on the 

 other hand, according to Payer and Rohrbach*, three stamens first of all appear after 



' On the nearly related Ccesalpineae see Rohrbach, Bot. Zeitg. 1870, p. 826. 



^ Compare the successive true whorls of Chara and Salvinia, pp. 279, 389. 



^ Compare also on this point Pfeffer, Jahrb, fiir wiss. Bot. vol. VIII, p. 205. 



* Rohrbach (Bot. Zeit. 1869, Nos. 50, sO however gives a different explanation to these observa- 

 tions from that mentioned here. The equal or greater distance at which the later stamens arise from 

 the centre of the flower is a distinct proof that one cannot in this case suppose that the parts are 

 produced in a spiral arrangement advancing from without inwards. 



