8 



HARD WICKE 'S S CIENCE - G O SSIF. 



with these, what are called Antheridia and Arche- 

 gonia. The former are scattered promiscuously over 

 the lower surface of the prothailium, but the latter 

 are more restricted in position and fewer in number, 

 being chiefly found in the thicker central parts among 

 the rootlets. 



Fig. 5. Frond of Parsley-fem 



{AZ/osorus cris^itis). 



Fig. 6. Portion of fertile frond 

 (magnified). 



Fig. 7. Fertile frond of 

 Osimmda re stalls. 



The Antheridia are developed from the lower free 

 surface of one of the cells of the prothailium, and 

 are composed of a single cell, or of two, one 

 being superposed on the other. In the interior of 

 these cells another is afterwards developed, which 

 becomes segmented, and each segment develops into 

 a minute vesicle, containing a spirally-coiled filament 

 called an Antherozoid, or Spermatozoid. When ripe, 

 the top of the antheridial cell drops off, and the 

 vesicles escape, each emitting its antherozoid, which 

 differs in form from those of mosses and liverworts, 

 and has numerous cilia. 



The Archegonia are usually produced on the same 

 prothailium as the Antheridia. Their external struc- 

 ture is that of very minute nipples, formed of four 

 collateral tiers of cells, with a passage down the 

 centre ; but the mouth of this passage or canal is 

 closed, until the archegonium is ripe, and then it 

 opens. This minute canal terminates, at its end 

 nearest the prothailium, in an embryo-sac. This sac 

 contains the germinal corpuscle, which is fertilized by 

 an antherozoid passing down the canal and coming in 

 contact with it. 



It seldom happens that more than one arche- 

 gonium on a prothailium becomes fertilized, the 

 abortive ones turning bro\^^^ in the canal and embryo- 

 sac. After fertilization, cell-division ensues in the 

 embryo ; and the result is the formation of a bud 

 producing foliage-leaves, which gradually become more 

 and more perfect till the true characteristics of the 

 fern are fully developed. 





Fig. 9. Pinnule of IVoodsia 

 (magnified). 



Fig. 10. Scale-fern {Ccterach 

 officinaruiit). 



Fig. 8. M'oodsia Ilvensis. 



Fig. II. Pinnule of Cetcrach 

 (magnified). 



These different stages of growth or development 

 may be observed by means of a microscope. Take a 

 frond with ripe spores and place it on a sheet of 

 white paper, with its front surface uppermost, and 

 leave it there for a day or two. After this the paper 

 will be found covered vrith a brownish dust : this is 

 composed of the spores. Then take a small piece of 

 porous sandstone ; moisten it with water, and place 

 upon it some of these spores. Place the sandstone 

 with the spores upon it in a shallow saucer of water, 

 and cover up the whole with a bell-glass. If kept in 

 a warm place and damp, but not too wet, some of 



