109 



Wind-pollination is ill adapted to the diversity of tropical 

 vegetation. Birches, oaks and hickories grow chiefly in northern 

 and temperate climates where plants of the same species are not 

 far apart and thus present comparatively large surfaces to 

 wind-borne pollen. A single ovule per flower is often associated 

 with wind-pollination, but the fused carpels suggest that the 

 ancestral plants had several ovules. Anatomical characters of 

 this group have recently been summarized by Tippo (3). 



CisTUS Group (Cistiflorae) — Sepals usually separate, 

 placentation usually parietal (that is, separate placentae), sta- 

 mens and ovules usually many. Parietal placentation precedes 

 axile placentation (2). 

 Cactales Papaverales Salicales 



(incl. Aizoaceae) 



Sarraceniales Passiflorales 

 Cistales (incl. Cucurbitaceae) 



Aristolochiales 

 This group and the following are connected through Frank- 

 enia-Dianthus , an affinity recognized by DeCandolle and by 

 Bentham and Hooker. They are also connected through Cacta- 

 ceae-Aizoaceae-Portulacaceae, a relationship recognized by 

 Schumann and also by Engler, though not expressed in the Eng- 

 ler system. 



DiAXTHUs Group (Dianthiflorae) — Placentation central 

 or basal, embryo often curved. 



Caryophyllales Polygonales Primulales 



Chenopodiales Piperales ? 



The following four groups have in nearly all cases axile 

 placentation, that is, placentae united in the center of the ovary. 

 In or near the Geranium Group must come the Ericales. 



Geranium Group (Geraniflorae) — Sepals usually united, 

 stamens usually many or in two w'horls. 



Theales Rutales Sapindales 



Ericales Geraniales Celastrales 



Mai vales 

 For the remaining groups the Engler sequence is approxi- 

 mately followed. 



