before the Linnean Society, May, 1878. 251 
branches or common trunks for future ramifications. We ma 
Suppose the center of the tree always to consist of those whicl 
tetain most of the ancestral characters, the lateral branches di- 
mo. 
of fixity. We may suppose this to be going on through mil- 
ons of ages, innumerable branches, whether near the center or 
More or less distant from it, ceasing to grow or to branch out, 
leaving gaps i rtiallv filled up, 
ps in the upper part of the tree, pa . : 
perhaps, in a few jomoben bk returning branches from the ies 
cumferential ones, and all decaying at the base, leaving only 
their upper extremities to continue the process in 
We should then have the present races re resented by = 
Countless branchlets forming the fatoppe summit “ry e 
eotyledonous tree—a hundred to a hundred and filty 
thousand ; i ecount species only, ten 
ti , perhaps, if we take into acc venus ae 
