CHAPTER XVI. 



REVIEW. 



The comparison of the development of the mosses and 

 liverworts on the one hand, with that of the ferns Equiseta- 

 ceae, Rhizocarpese, and Lycopodiaceae on the other, dis- 

 closes the most complete uniformity between the fruit- 

 formation on the one hand and the embryo-formation on the 

 other. The structure of the archegonium of the mosses — 

 the organ within which the fruit-rudiment is formed — is 

 exactly similar to that of the archegonium of the vascular 

 cryptogams, the latter being that part of the prothallium in 

 the interior of which the embryo of the frond-bearing 

 plant originates. In both the large groups of the higher 

 cryptogams there is a cell which originates freely in the 

 larger central cell of the archegonium, by the repeated 

 division of which (free) cell, the fruit of the moss and the 

 frond-bearing plant of the fern are produced. In both, 

 the divisions of this cell are suppressed and the arche- 

 gonium miscarries, unless, at the time of the opening of 

 the top of the latter, spermatozoa find their way to it. 



Mosses and ferns therefore exhibit remarkable instances 

 of a regular alternation of two generations very different 

 in their organization. The first generation — that from the 

 spore — is destined to produce the different sexual organs, 

 by the co-operation of which the multiplication of the 

 primary mother-cell of the second generation, which exists 

 in the central cell of the female organ, is brought about. 

 By this multiplication a cellular body is produced which in 

 the mosses forms the rudiment of the fruit, and in the 

 vascular cryptogams, the embryo. The object of the 



