134 



THE LIVING CYCADS 



leaf of the seedling in some cases not reaching more than 

 a tenth of the length of the leaves of adult plants. The 

 number of leaflets is smaller. In Ceralozamia the first 

 leaf usually has four leaflets, while the leaves of large 

 plants may have as many as a hundred leaflets. The 

 number of leaflets increases steadily as the plant becomes 

 larger, until, in this respect as in the case of the number 

 of leaves in a crown, it attains the approximate norm 

 of the species. 



In seedlings the margin of the leaflet often dift'ers 

 strikingly from that of the leaflet of an old plant. Dioon 

 cdnle may be taken as an example (Figs. 74-76). The 

 leaflet in the seedling has a spiny margin, the spiny char- 

 acter being most conspicuous during the first four or 

 five years; the number of spines then diminishes slowly 

 but does not disappear completely until the plant has 

 reached an age which may be estimated at twenty or 

 thirty years. 



In this connection it is interesting to note that the 

 seedling leaves of Dioon spinulosum have the same spin\- 

 character, but that the plant retains it as long as it lives. 

 Many would regard this as an illustration of recajMtula- 

 tion— ontogeny recapitulates phylogeny, or the history 

 of the individual is the history of the race— and would 

 claim that Dioon edulc is the ofi"spring of D. spinulosum, 

 and that D. ediile in its earlier development is passing 

 through a stage which characterized its ancestor. In 

 the case of Encephahirlos AUcnsleinii and E. cajjcr a 

 difference in leaf margins is enough to confuse a ta.x- 

 onomist in his diagnosis. E. Altcnskinii has leaflets with 

 spiny margins, and the character is supposed to persist 

 throughout the life of the individual. E. caffcr shows 



