1895.] Present Problems in the Cactacee. 221 
produced a thousand species, with some genera including over 
_ two hundred species; and in addition has developed hundreds 
of forms of spines, hundreds of modifications of tubercles and 
ribs, and hundreds of variations upon other points of its struc- 
ture. Clearly we must allow for differentiations which are 
without reference to use. He who believes that differentia- 
tion depends solely upon the preservation of favorable over 
unfavorable variations can find in this family less support 
ency to variation led along certain lines by little known 
though omnipresent principles of inertia and segregation, 
these lines cut off by natural selection when they are opposed 
to adaptation (z. ¢., unfit), but allowed when competition is 
absent to persist whenever not opposed to adaptation (7. ¢., 
not unfit, or indifferent) as well as when positively adaptive; 
until finally when competition comes into play the positively 
adaptive lines triumph over the indifferently adaptive and 
natural selection has wontheday. I believe the Cactacez are 
in the condition in which there is little competition, and that 
there are present many indifferently adaptive as well as pos- 
itively adaptive features of structure, and that the former 
sometimes are not much behind the latter in degree of dif- 
ferentiation. 
Smith College, Northampton, Mass. 
