INTRODUCTION. XXVll 



plant could not have lived one day so exposed in the 

 open air ; in the phial, it had lived a year, had 

 renewed its fronds, and looked healthy. How was 

 this effect produced ? 



Who has regarded Nature without perceiving the 

 word CHANGE legibly engraven on every object ? 

 Throughout creation there is a perpetual decay, and 

 a perpetual renovation. Death is the result of hfe, 

 for life contains within itself the germ of death. This 

 fact is so obvious, that it were idle to adduce proofs. 

 There are many active agents in this change ; and it 

 may be observed, that the office of every agent is to 

 hurry forward the eternal round : the sun is equally 

 the source of life and death : wind, rain, heat, cold, 

 all are perpetual agents in this one work. 



If we seek for the accessory circumstances most 

 favourable to the rapid and healthy growth of Ferns, 

 and refer for the information to Nature herself, we 

 shall generally find them in protection from the sun's 

 rays, in the uniformity and excess of atmospheric 

 humidity, in the absence of extremes of heat and cold, 

 in the gradual transition from one to the other, when 

 these extremes do occur, and, finally, in that perfect 

 stillness of the atmosphere which is rarely realized in 

 Nature, except in caves, fissures of rocks, wells, and 

 a few similar situations : the opposites of all these are 

 the agents of decay and destruction ; the excess of 

 atmospheric aridity; sudden alterations in the tem- 

 perature, as in the frosts of spring ; excessive heat ; 

 high and boisterous winds. Were not this law of 



