from ovary superior to half inferior, to wholly inferior; 

 from placentation axile to parietal or central; 

 from many seeds to few. 



These are, in general, changes in the direction of greater 

 care of the next generation. 



Stamens 



from numerous to two whorls, to one whorl; 



(indicated, respectively, by three, two or one figure on 

 each side of the flower) ; 

 from separate to united, 



(by cohesion of filaments, or of anthers, or by adhesion 

 to petals). 



With more effective methods of pollination, less pollen 

 is needed. 



Petals (indicated by dotted lines) : 



from separate to united ; 



from regular to irregular. 



These are changes in the direction of increasing adapta- 

 tion to insect visitors. 



On page 74, Torreya, July-August, 1926, is a diagram of the 

 Evolution of Dicotyledons according to Hutchinson. Though 

 not adopting the main division into woody and herbaceous 

 plants, the diagram opposite in other respects is not altogether 

 different. 



In the Engler system, the group Parietales appears to occupy- 

 a somewhat advanced position. This, however, must be con- 

 sidered as due to the requirements of a linear sequence, as this 

 group connects so closely with the Magnolia group. Similarly 

 the great family, Myrtaceae, is here placed nearer the base. 

 This appears to make other connections more natural, and thus 

 Australian plants, as w^ell as animals, may be in general more 

 primitive. 



For the definition of species, nomenclatorial types are im- 

 portant. From the point of view of the classification of families 

 the idea of structural types is of chief concern. Early system- 

 atists often reversed families, as when Cactaceae were begun 

 with Cereus, or Gramineae terminated with Bambusa. Thus 

 groups were, so to speak, suspended without any connecting 

 link with others. It is important to know what is the essential 



71 



