BOTANY OF THE LIVING PLANT 



An early line of specialisation led towards a cyclic arrangement 

 of the parts, their number becoming at the same time more definite. 

 The outer whorls were differentiated as the protective calyx and 

 the attractive corolla. These steps are illustrated among the Ranun- 

 culaceae, which include both hemicyclic and cyclic flowers (Figs. 1 88, 

 189). The best examples of the cyclic state are, however, found among 

 the more advanced types, where that feature is constant (Figs. 

 187, 192). Once the cyclic flower was established, other biologically 

 effective modifications followed. The sepals became united into 

 the mechanically stronger gamosepalous calyx. The petals also 

 became coherent, thus acquiring mutual strength, and at the same 

 time fencing round the honey-secretion at its base. Moreover the 

 gamopetalous corolla has often assumed forms that suit the con- 

 venience of the insect-visitors : colours and odours that attract ; 

 and it even shows distinctive lines that guide the eye to where the 

 honey lies. The stamens become adherent to the corolla-tube. 

 Such features go habitually with that lop-sided or zygomorphic 

 development which secures a convenient alighting platform, and 

 ensures a definite position for the visitor. The result of this precise 

 mechanism is that there is economy in the amount of pollen necessary 

 to make pollination a reasonable certainty. 



So long as the flower is not highly specialised a large production of 



pollen, and a large number of carpels and ovules will be advantageous 



or even necessary, for this will multiply the chances of successful 



propagation. It is then natural to find that pleiomery of stamens 



and carpels is common in non-specialised types. For instance, the 



Ranunculaceae (Figs. 188, 189), and Rosaceae (Fig. 191), the Lime, 



and the Mallow are all polypetalous flowers of radial construction, 



and they have as a rule numerous stamens and carpels. But their 



haphazard methods of pollination and of seed-distribution entail 



waste. Economy comes with specialisation, such as is seen in the 



Gamopetals, and in the more highly adapted Monocotyledons. In 



them meiomery appears both of stamens and carpels. The former 



may be reduced from the fundamental number of the flower to two 



Veronica (Fig. 193), Salvia, Cypripedhwi], or to only one (Centranthus, 



hrhis, Ginger). The carpels of highly adapted flowers often number 



only two, and they may be reduced to one, as in the Papilionaceae. 



I he ovules themselves are frequently solitary where the seed is large, 



and its chances of distribution and germination are good, as they 



in the Coconut and Cherry, and in the Grasses. Thus there is 



a biological rationale underlying pleiomery and meiomery, both of 



