128 STUDY OF COMMON PLANTS. 



V. Comparison of the archegonia and antlieridia of 

 liverworts and mosses. 



VI. Alternation of generations as seen in mosses and 

 liverworts compared with the ferns and other 

 vascular cryptogams. This will naturally be 

 postponed until after the studj-- of the latter 

 groups. It will be found that in the ferns the 

 oophytic generation is reduced to a green pro- 

 thallium, and in the club-mosses and their allies 

 a still further reduction takes place. 



VII. Origin of the calyptra of mosses. 



REVIEW AND SUMMARY. 



Mosses and liverworts occupy an intermediate position 

 between the strictly cellular cryptogams, represented by 

 the algse, and the vascular cryptogams, which 

 ohaiacter. include the ferns, club-mosses, etc. The sim- 

 iverworts, p^gg^ forms of liverworts are cellular structures, 

 showing little if any advance in differentiation beyond that 

 attained by many algse. Certain ones are characterized 

 by aquatic habits. Furthermore, in their modes of repro- 

 duction, there is much to remind one of what is observed 

 in some of the algse. 



Considering, therefore, structure, habits, and reproduc- 

 tion, we must regard the liverworts as next above the 

 algse in the scale of development. It has been 

 gronpa, assumed, aud there is much to indicate that the 



°^^°'' conception is a truthful one, that certain algse 



in the course of time have acquired terrestrial habits, and 

 with them, corresponding to their changed conditions of 

 life, the peculiarities of form and structure characteristic 

 of liverworts. The simpler mosses closely resemble the 



