INTRODUCTION. XIX 



Ferns, mosses, and all kinds of cryptogamous plants, 

 seem to spring up spontaneously in these cases ; and 

 the surface of the earth speedily becomes clothed not 

 only with a beautiful but a highly interesting vege- 

 tation. The raising of Ferns from seed, in the manner 

 hereafter described, offers a ready way of ascer- 

 taining beyond question the value and limits of each 

 species. 



It has often been considered somewhat unaccount- 

 able that plants should thrive when deprived of air. 

 I believe a philosopher would smile at the idea of a 

 vacuum existing in a vessel containing abundance of 

 earth, water, and living vegetables ; but let us con- 

 sider the subject, without reference to any philo- 

 sophical inquiry. It must, then, be understood as an 

 unquestionable fact, that in closing the vessel no 

 attempt is ever made to exclude the air which it con- 

 tains, or even by any experiment to diminish its 

 quantity ; therefore, admitting the property of air to 

 press equally in all directions, we must take it for 

 granted that there is as much air in the vessel as in 

 an equal space outside the vessel ; and so, the idea 

 that the ferns are living without air not being based 

 on fact, requires no refutation. The next source of 

 wonder is, that a fern should thrive deprived of that 

 fresh air, or that change of air, which, in a state of 

 nature, it is constantly enjoying. The term fresh 

 air, though so continually used, has no very definite 

 meaning. If it applies to air that has not been 

 breathed by animals, I believe we shall find that 



