98 AMERICAN FERN JOURNAL 
extent, a much larger fern-flora might reasonably be 
expected. For heat combined with moisture forms the 
combination which the fern family finds best suited to 
its requirements. It is where such conditions exist 
that “fern paradises” are found. If ferns make their 
homes where other conditions prevail, there is required, 
or rather, to speak more correctly, there is developed 
a modification of form and habit. 
The result of actual conditions is the development in 
the cool fog-belt of a luxuriant growth of Polystichum 
munitum and Pteris aquilina, which prevail abundantly 
from one end of it to the other, and of a very limited 
number of other species. At the other geographical 
extreme, the arid south, there is a greater number of 
species, but the abundance of individuals admits of no 
comparison with the fecundity of the northern coast. 
The open pine intervals of the forests support an under- 
growth of the same Pteris that abounds in the north, 
but in stature, in the structure of its contracted fronds, 
its aspect is very unlike the robust and tall coast form. 
Pteris aquilina is the only fern that forms a growth over 
extended areas in the south. The others grow in the 
select places to which their specialized structure and 
habits of life fit them. They seek the shelter of boulders, 
of shrubs, and of rock crevices, and are thus able to 
exist under very unfavorable conditions. As there 
are only special places in which they are able to grow, 
and these limited in respect of the whole area, there is 
a comparative scarcity of individuals; in some cases 
more than a comparative, a positive, scarcity. I have 
in mind a species (Cheilanthes fibrillosa) of which the 
type collection is the only one known, yet its validity 
has never been questioned by fern students. Of another 
(C. Parishii) there have been but two scanty collections, 
made at an interval of 20 years, and both in the same 
canyon. These two are, at least so far as this slender 
knowledge indicates, endemics, but there are two other 
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