SOUTHERN CALIFORNIA FERNS 103 
A third class of the southern California ferns includes 
those with perennial foliage and a continuous period of 
growth. Of necessity they are confined to situations 
which afford them a reliable supply of water throughout 
the entire year, and where the extremes of seasonal 
variations do not, at any period, entirely prevent growth. 
These conditions may vary within certain limits, so that 
the activity of life may be accelerated or diminished at 
certain periods for some of these ferns; and in this respect 
these vary among themselves, but they must at no time 
prevent the verdancy of the foliage, or suspend the 
activity of the vital functions. 
Two ferns which are at the outer limits of this class 
are Nephrodium rigidum argutum and _ Polystichum 
munitum. These ferns, which are found throughout 
the whole length of the state, and northward to British 
Columbia, and even one of them, to Alaska, in the southern 
part of the state grow on lightly shaded canyon slopes, 
and have a range of altitude which does not expose 
them either to the intense heat of the lower hills, or to 
the great cold of the higher mountains. Their water 
supply is greatest in late spring and early summer, and 
it is at this period that they make their most vigorous 
growth; in the late summer their growth is checked by 
the diminished moisture in the soil, and in winter by the 
lower temperature. They, therefore, at least for a part 
of the annual cycle, require a degree of economy in the 
conservation of their water content. This results in 
fronds intermediate in form and texture between those 
of ferns which must live on the scantiest allowance of 
water, and those which have it in abundance. 
Adiantum capillus-veneris illustrates the other ex- 
treme in this class. It affects the face of well-shaded 
cliffs, over which drips water from a perennial source, 
and being more sensitive to cold, it is limited to a much 
narrower altitudinal range than the two species last 
