THE EVOLUTION OP PLANTS 2OQ 



142. Derivation of New Types.- Attention should here 

 again be called to the fact that the theory of evolution does 

 not teach that one given species becomes transformed into 

 another, but simply that new species are descended from 

 older forms which may or may not continue to exist. It 

 is not supposed, for example, that ferns developed into 



FIG. 93.- Cycadcoidea dacotensis. Semi-diagrammatic sketch of a 

 flower (bisporangiate cone), cut longitudinally; one sporophyll folded, and 

 one (at the right) arbitrarily expanded. At the center is the apical, cone- 

 shaped receptacle, invested by a zone of short-stalked ovules and inter- 

 seminal scales. The pinnules of the sporophylls bear the compound 

 sporangia (Synangia). Exterior to the flower are several hairy bracts. 

 About three-fourths natural size. (After Wieland.) 



cycads, and cycads into higher gymnosperms, but that 

 there has been an unbroken line of descent (possibly more 

 than one) in the plant kingdom, that closely related forms 

 (like ferns and cycads) have descended from a common 

 ancestral type which may or may not now be found. We 

 must not, in other words, expect necessarily to find in 



