43G HOIMEISTEH, ON 



The contrast however is not so marked as it appears at first 

 sight. The apparently unlimited life of the leaf-bearing 

 moss depends merely upon continual renovation. Pheno- 

 mena of a similar kind are met with in the sprouting 

 prothallia of Polypodiacese and Equisetaceae. In the lowest 

 liverworts (Anthoceros and Pellia) the structure of the 

 fertile shoots is less complicated, and their duration little 

 longer, than that of the fruit. On the other hand the 

 ramification of the prothalliuui of the Equisetaceae is very 

 variable ; its life is not of shorter duration than that of an 

 individual shoot. 



It is a circumstance worthy of notice that in the second 

 or spore-forming generation of mosses and ferns, compli- 

 cated thickenings of the cell-walls usually occur (witness 

 the teeth of the peristome in mosses, the capsule-wall and 

 the elaters in liverworts, and the vessels in ferns), whilst in 

 the first generation these thickenings are rare and excep- 

 tional. 



An unprejudiced consideration of the subject will show 

 that the separation into two groups only of the plants com- 

 prising the mosses on the one hand, and the liverworts 

 (Jungermanniae, Marchantieae, Anthoceroteaa, and Riecieae) 

 on the other, is not natural. There is no marked feature 

 by which these two groups can be distinguished. It is 

 true that a pro-embryo like that in the mosses is wanting 

 in most of the genera of liverworts, especially in all the 

 leafless ones. Many leafy Jungermamrieae, however, espe- 

 cially the true Jungermanniae, exhibit the phenomenon of 

 the conversion of the germinating spore into a single row 

 of cells, one of which cells, by repeated divisions in all 

 three directions of space, becomes the rudiment of the leafy 

 axis. This phenomenon is as well marked as in any of the 

 mosses. The outward form of the antheridia and arche- 

 gonia in the two groups differs very slightly. The first 

 stages of development of the fruit-rudiment of the mosses 

 on the one hand and the Jungermanniae on the other, are, 

 it is true, very different. In the former the longitudinal 

 growth is caused by the continually repeated division of a 

 single conical apical cell of the organ, by means of septa 

 inclined alternately in two directions ; in the latter this 



