2l8 



HEREDITY AND EVOLUTION IN PLANTS 



Angiospermous characters, and therefore, while they are not 



to be considered as the ancestors of 

 the Angiosperms, it is probable that 

 they and the modern dicotyledons 

 are both descended from a common 

 branch of the ancestral tree. Among 

 modern plants, the flower of the 

 magnolias most closely resembles 

 that of Cycadeoidea in the spiral 

 arrangement of its stamens and 

 pistils (Figs. 101 and 102). Just 

 what significance should be attached 

 to that fact has been disputed by 

 students of morphology. The older 

 view of the systematists regarded the 

 primitive flower as more complex in 

 structure, with pistils, stamens, and 

 floral envelopes arranged spirally in 

 centripetal or aero petal succession on 

 a fleshy axis, as in Magnolia and other 

 flowers of the order Ranales; other 



types of floral structure were con- 

 FIG. toz.-Magnolia sidered ^ derived from this one by 

 Flower with perianth .... 



removed, showing the reduction. This is often referred to 

 compound pistil, and four as the "Strobiloid theory of the 



of the stamens. Most of fl ower " (C/. pp. 132 and 134). 



the stamens have been 



removed so as to bring A m rc recent VieW ^COgniZCS 



out their spiral arrange- that simple staminate or pistillate 

 ment as shown by the flowers may, in some cases, be in- 



scars at the points of ^ ^ derived by reduction 



attachment. (Cf, Fig. 



IOIt ) from more complex forms, but re- 



gards the primitive flower as uni- 



