CHAPTER XVI. 



REVIEW. 



The comparison of the development of the mosses and 

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

 cese, 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 archegoniuni 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 



