REPRODUCTION IN PLANTS. 



125 



These cells are liberated, when they burst, and give exit to 

 true spermatozoa in the form of ciliated spiral filaments. 

 The female organs are also placed upon the under surface 

 of the prothallus, and also have the form of cellular pro- 



Fig. 37- A, Portion of the frond of Polypodium vulgare, showing the organs of 

 fructification. B, Spore-cases of the same, magnified. C, Spore of a Fern, greatly 

 enlarged. D, Cellular prothallus of a Fern, produced by a spore (s\ and giving 

 off a root (r). 



minences. The cells of these prominences are so arranged 

 that they form a canal, leading down to a large central cell 

 or ovule. 



The spermatozoa liberated from the male organs pass 

 down the central canal, and gain access to the ovule. 

 As the result of this, segmentation of the ovule is set up, 

 and an embryo is produced from which the frond of the 

 ordinary fern is developed, the prothallus perishing when 

 this is accomplished. 



The sequence of phenomena here indicated may in some 

 respects be fairly compared with those formerly alluded to 

 under the head of " alternation of generations." The 

 " spores " produced in the spore-cases of the ordinary fern 

 are to be regarded simply as buds, since they are not pro- 

 duced by any generative act, whilst they have the power of 

 developing themselves without contact with a second dis- 



