CYCADALES 



95 



leaflets are reflexed on the rachis. The other three are not so easy. 

 In Ceratozamia the leaflets are always entire (integerrima) , a char- 

 acter very rare in Zamia and found only in a part of the species of 

 Encephalartos. By adding the histological characters of the leaf, any 

 indefiniteness in the identification could be removed. 



The leaflets of young and adult plants are usually quite different, 

 so that some botanists regard the juvenile form as evidence in favor 



Fig. 87. — Dioon edtile: young crown, showing perfectly erect vernation. Tn the 

 greenhouse of the University of Chicago. 



of the theory of recapitulation, which means that ontogeny recapitu- 

 lates phylogeny, or the history of the individual recapitulates the 

 history of the race. 



Dioon spinulosiim, in the seedling and in young plants, has a leaf 

 with a long naked petiole and lowest pair of leaflets nearly as large 

 as the rest; whfle in older and adult plants the leaflets are more and 

 more reduced until, at the base of the leaf, they are scarcely more 

 than spines. 



In Dioon edith leaflets of seedlings and young plants have a spiny 



