100 AMERICAN FERN JOURNAL 
continuing its active functions for the whole period of 
its life. In the different regions to which ferns have 
become acclimated other habits of life have become 
necessary. In cold climates the low temperature may 
destroy the aerial parts, or may suspend their functions, 
so that all the operations of life,—growth and the re- 
productive processes-—must be carried out in the summer 
months. In our region this is the case with Pteris, 
which is cut down by the first frost. But the ferns we 
are now considering have an opposite life-problem to 
solve. They have at all seasons sufficient heat and sun- 
light, and for half the year an excess. Their greatest 
need is water. Our arid ferns meet the situation by 
making their growth in the winter, at which period of 
the year the rains occur, and by passing the summer in 
dormancy. But these rains are small in amount at 
any one time, they are uncertain, and the moisture is 
liable to be speedily evaporated by drying winds, Their 
fronds, therefore, unfold at once as soon as moistened 
by the first shower and resume life at the point where 
they dropped its functions, perhaps months ago. How 
long this active life may continue depends wholly upon 
the meteorological conditions. So long as moisture is 
attainable there is no cessation; but as soon as it fails 
active life is suspended. In this condition the fern 
appears dead; the frond is dry and crumbles in the 
fingers, the stipe and rhizome are brittle and break up 
in handling. These resting fronds assume various 
forms. Many curl up into more or less compact balls, 
exposing to the air the back of the frond,. which 
is the most heavily protected. A study of the mechanics 
by which this rolling up is effected would be of interest. 
Perhaps it has been made, but, if so, I have never happened 
to read of it. If not, it is well worth making. The 
same phenomenon is familiar in the Mexican Selaginellas, 
which are sold under the name of “resurrection ferns,” 
" AES May eh Gas VER one Lira 
Sey OE Re eee eT ne REIDY By ke, ot yi 
