NATURE STUDY. 
146 
proportion between the number of genera and species as well 
as of individuals in the first and third families. The adder- 
tongue family can show only three genera and a few over 
twenty species against the seventy or more genera and three 
thousand or more species of the polypody family. As to 
the intermediate family, it possesses, be¬ 
side Osmunda, with six species, one other- 
genus, Todea, with four known species, 
native of Australasia and South Africa. 
It is not so much the fact of this dispropor¬ 
tion as the cause of it which is of vital in¬ 
terest. The archaic forms have one by 
one passed away because they were not 
adapted to the new conditions of life. The 
few that remain are those which have suc¬ 
ceeded in temporarily staving off impend¬ 
ing destruction by a partial adaptation to 
modern environment. 
On the other hand, the immense in¬ 
crease in numbers in the family of which 
Polypodimn is the type, is the result of a 
high degree of specialization, amounting, 
in fact, to adaptation to almost any and 
every condition of plant life in the present 
state of the earth’s surface. The possible 
habitats of Ophioglossum and Botrychium 
fare, by comparison, very restricted. With 
few exceptions, the species require a rich 
soil, partial, but not excessive, shade, and 
the non-intrusion of stronger plants. On 
the other hand, the Polypodiacese have 
succeeded in accommodating themselves 
to habitats of extremely diverse character. 
From Ceratopteris, (horn-fern) , which is strictly aquatic, 
the possibilities of habitat range through all degrees of 
moisture and dryness to the bare cliff, where 
Fig. 1 
