372 ON EEPRODUCTION. 



species (see page 37). Although these spores are so small 

 they are nevertheless endowed with an extraordinary- 

 power of retaining their vitality ; and, being easily wafted 

 by currents of air, readily account for the wide geogra- 

 phical range of some species of Ferns. When naturally 

 or artifically placed under favourable conditions they burst, 

 and expanding in the form of a simple oblong cell, on 

 which other cells are successively developed, ultimately 

 form a thin green membrane called the proihallium, 

 which, when arrived at full size, is of a reniform cordate 

 shape, or sometimes bilobed, or obcordate, varying from 

 about 5 to ^ inch in diameter, and adhering to the surface 

 on which it vegetates, it has much the appearance of a 

 small foliaceous lichen or Marchantia. In time a small 

 bud makes its appearance near the base of the prothal- 

 lium, which increases in size, and ultimately a small frond 

 is produced, which is succeeded by others successively 

 larger, thus becoming a plant. 



The increase of the prothallium and sprouting of the bud 

 is readily seen by the naked eye, and the cultivator is 

 satisfied with the result; but he finds himself often dis- 

 appointed, for after having obtained abundance of prothallia 

 from many different species, they nevertheless do not 

 always produce a bud germ. This is now supposed to be 

 explained by the discovery made in 1848 by Count Suminski, 

 a Polish botanist, that Ferns possessed organs analogous 

 to the stamens and pistils of flowering plants, and that 

 these were produced on the under side of the prothallium ; 

 they are represented by two kinds of cells, one called 

 Antheridia and the other Archegonia. The first (of which 

 there are generally between 30 and 40) consist of round 

 cells, which contain vermicular spermatozoids that issue 

 from the cells when arrived at maturity. The cells of the 



