6o8 PHANEROGAMS. 



of divergence, as in most trimerous or pentamerous calyces, this can be indicated by 

 placing the angle of divergence after the number of the members ; thus the formula for 

 Linaceae would be S^^'^j^^P^^St^.C^. If, on the other hand, the members of a whorl are 

 formed in succession from front to back, this may be shown by an arrow pointing 

 upwards t, as in the formula for Papilionaceae S^] P^\ St^\ +5! C^. If they are formed 

 in succession from back to front, the arrow may be made to point downwards j, as 

 in the formula for Reseda 5„i P„l Stp[ + q[ C,-, where the number of the parts is expressed 

 by letters instead of figures in consequence of its variability \ 



4. Order of De'velopment of the Parts of the Flower. The foliar structures arise on the 

 axis of the floral shoot, as on other axes, in ticropetal order below the growing apex. It 

 is however not uncommon in the formation of flowers for the apical growth of the axis to 

 cease altogether or to become extremely slow, while the receptacle continues to increase 

 in breadth, and to develope transverse zones of intercalary growth. When this is the 

 case the acropetal order of development is disturbed, and new whorls may become 

 interposed between those already in existence. But even within the same floral whorl 

 the individual members may be formed in a very different order of succession, according 

 as the zone of the receptacle which bears the floral leaves is developed in a uniform 

 manner all round (as in polysymmetrical flowers) or more rapidly on the anterior or 

 the posterior side (which is especially the case in monosymmetrical or zygomorphic 

 flowers). 



In flowers with a spiral arrangement of their parts^, disturbances of the acropetal 

 order of development are of less importance the more numerous the parts with a spiral 

 arrangement, and the longer the apical growth of the floral axis continues. Those mem- 

 bers which have a spiral arrangement arise one after the other in ascending order ; the 

 angle of divergence may either be constant or may change. Thus, according to Payer, 

 in Ranunculaceae and Magnoliaceae the perianth-leaves and stamens arise in a con- 

 tinuous spiral, but each turn of the spiral consists of a larger number of stamens 

 than of perianth-leaves ; thus, e. g., in Helleborus odorus, where all the organs of the 

 flower are arranged spirally, the corolline turn includes only thirteen petals, while 

 each turn of stamens numbers twenty-one. According to Braun the turns of the 

 calyx of Delphinium Consolida have a ^5 arrangement^; the divergence then under- 

 goes a small change, but without materially deviating from ^5 ; the first turn with this 

 altered arrangement is the corolla ; the three following ones are the stamens, and the 

 spiral terminates with a single carpel. In the section Garidella of Nigella the first of the 

 turns with a ^5 angle of divergence is the calyx and the second the corolla; then follows 

 a slight change in the angle to ^g? the stamens forming one or two turns with this 

 arrangement; and the spiral closes with three or four carpels. In the section Delphi- 

 nellum of Delphinium the calyx constitutes a turn with ^s) the corolla one with ^g 

 angle of divergence ; then follow two or three turns of stamens with the angle very 

 near %, the spiral closing with three carpels. In the section Staphisagria of the same 

 genus, and in Aconitum, the calyx forms a turn with ^5, the corolla one with % angle ; 

 the stamens stand in one or two turns with the divergence ^21 or '734 > concluding 

 with three, five, or rarely a larger number of carpels. It must be noted in reference to 

 these arrangements that the members of successive turns stand in orthostichies when 

 the angle of divergence remains constant ; but that the orthostichies pass into oblique 

 rows when the divergence undergoes a small change. 



The first thing to observe in cyclic flowers (/. <?. those in which the parts are arranged 

 in whorls) is the order of formation of the whorls with respect to one another, and then 



* See Payer, Organogenic de la fleur ; also the next paragraph. 



2 Compare Payer, Organogenie de la fleur, pp. 707 etseq.; and Braun, Jahrb. flir wissensch. Bot. I, 

 Ueber den Bliithenbau der Gattung Delphinium. 



^ Compare with this what is said below respecting sepals and petals which are formed with the 

 angle of divergence Y3 and Yg. 



