ANGIOSPERMS. 



53' 



manner all round (as in polysymmctrical 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 i, disturbances of the acropetal 

 order of development are of less importance the more numerous the parts w ith 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 ^Nlagnoliaceae the perianth-leaves and stamens arise in a continuous 

 spiral, but each whorl of stamens consists of a larger number of members than the 

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

 flower are arranged spirally, each whorl of the corolla consists of only thirteen petals, 

 while each whorl of stamens numbers twenty-one. According to Braun the whorls of 

 the calyx of Delph'mium Consolida have a % arrangement - ; the divergence then under- 

 goes a small change, but without materially deviating from %; the first whorl 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 

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

 a slight change in the angle to "^ ,-, the stamens forming one or two whorls with this 

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

 nellum of Delphinium the calyx constitutes a whorl with '^/g, the corolla one with % 

 angle of divergence ; then follow two or three whorls 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 whorl with %» the corolla one with ^, g angle ; 

 the stamens stand in one or two whorls with the divergence Vsi 01* ^'Ai 5 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 whorls 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 [i.e. those in which the parts are arranged 

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

 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 

 cnlycimim 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 Compositgp, Dipsacaceae, Valerianaceap, and Rubiacese. 



One of the most remarkable deviations from the general rule of the order of develop- 

 ment of the floral whorls occurs in Primulaceae, 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. Pfefl'er, who has observed this order of development (Jahrb. flir 

 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 outgroAvths of the stamens (a posterior ligular structure), such as, for 



' Compare Payer, Organogenie de la fleur, p. 70; e/ seq. ; and Braun, Jahrb. fiir wis-ensch. Bot., 

 Ueber den Bltithenbau der Gattung Delphinium. 



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

 angle of divergence Y3 and Y5. 



2 Compare Plofmeister, AUgemeine Morphologic,, pp. 436 ei seq., where Payer's ol servations on 

 this point will also be found. 



>I m 2 



