OTHER PORMS OF ALTERNATION. \b\ 



The development of tlie pollen in tlie anther, and the 

 embryosac in the ovule of the former division, may be shown 

 to present a distinct analogy in essential points with the 

 antherozoids and archegonial corpuscules in the protliuUium 

 of the latter, that is, in the cellular mass which is first 

 formed in the germination of the spore. The resemblance, 

 it must be admitted, does not lie on the surface ; the short 

 summary given in the second Chapter shows but little 

 prima facie similarity between the cases, but it exists not 

 the less in those points which are of most essential import- 

 ance in the reproductive process, and a closer comparison 

 will indicate many points of analogy. 



Thus, starting w^th the assumption that the spore-bearing 

 capsule of the fern corresponds to the ovuliferous carpel of 

 a flowering plant, it is interesting to observe that they are 

 both modifications of leaves ; though tliis is a subject on 

 which it is unnecessary to enlarge here, as full reference has 

 already been made to the circinate vernation and other 

 points of relation between the spore-cases and the ordinary 

 leaves of ferns, in comparing these plants with mosses. 

 The connection of the capsules with the fronds has a paral- 

 lel in the case of the Riiscus aculeatus. But the principal 

 analogies of the reproductive process lie in the changes oc- 

 curring in the germination of the spore itself, and in the 

 transformation of the ovule into the seed. The main 

 feature of this development is that in the cellidar substance 

 of the ovule, or the cellular outgrowth of the spore (as the 

 case may be) minute capsules are generated, — known respec- 

 tively as embryosac and archegonium, — witliin which pecu- 

 liar corpuscules are formed, fitted to become tlie subjects 

 of impregnation. These corpuscules, whicli, from the tes- 

 timony of some able observers, appear to have at first no 

 distinct boundar}^ walls, are converted by fertilization into 

 true cells, and afterwards by a process of endogenous growtli 

 into clusters of cells. The part of the cell-mass first formed 



