THE EMERGENCE OF THE FLORAL WHORLS. 185 



outgrowths from the stamens. Mj own observations tend 

 to confirm those of Dr. Masters, that it is an exceptional fact, 

 and not constant. It appeared to him " that in hysimachia 

 Nummularia the petals did really sometimes (but not always) 

 precede the stamens in their development." 



The stamens emerge before the pistil, and if there be two 

 whorls to the androecium, it is the sepaline whorl which 

 appears first; though the fully developed stamens sometimes 

 assume a position, as already explained, within the petaline, 

 as in Geraniacece. Like the corolla and staminal whorls, the 

 carpellary appears all at once, and last of all. 



With reference to the emergence of the individual parts 

 of the whorls, it is an almost invariable rule that those of the 

 outermost whorl of the perianth or calyx, if it consist of three 

 or five parts, rise centripetally in succession according to the 

 laws of phjilotaxis. Thus, if the calyx be pentamerous, its 

 parts invariably emerge in quincuncial order, thus consti- 

 tuting a cycle of the f type. If it be trimerous, as in Mono- 

 cotyledons, it is a cycle of the § type. If, however, it be 

 tetramerous, then the parts emerge in decussating pairs, as 

 in Tamarix tetrandra, Sparmannia, Philadelphus, and the 

 sepals in the Gruciferce* This clearly shows that a normally 

 tetramerous calyx is the result of the combination of two 

 pail's of leaves, corresponding to two nodes, the internode 

 between the pairs being suppressed. 



The parts of the inner whorl of the perianth or petals of 

 the coroUa, as also those of each staminal and carpellary 

 "whorl, almost invariably emerge simultaneously if the whorls 

 be regular ; though pronounced differences may occur in the 

 case of irregular flowers. Similarly, when- there is a strong 

 spiral tendency, as in the RanunculacecB, members may arise 



* The lateral sepala, thoagh overlapped by the other pair, are the 

 first to receive their vascular cords from the axis. 



