198 CRYPTOGAMS 



LIVERWORTS AND MOSSES (BRYOPHYTES) 



462. The account of Chlorophyllous plants was inter- 

 rupted at the end of the section on Red Seaweeds. A 

 series of colorless forms (Fungi) was then introduced, in 

 general structure and often in detail closely resembling 

 Algae. We return to chlorophyll-bearing plants at a point 

 where the ascending line of vegetable life leaves the 

 waters to become henceforward very largely terrestrial. 



463. The words " line " and " series " are not to be understood in 

 too restricted a sense. For example, in Algae several seeming lines of 

 progressive development, running more or less side by side, are to be 

 discerned ; and the same may be said of any large group of plants. 

 Moreover the " line " or " series " is never continuous, is in fact 

 merely a succession of considerably separated groups, through which 

 run certain general principles of structure. In the grand series begin- 

 ning with unicellular Algae and ending with Flowering Plants, many 

 breaks occur. That is, at certain points new features appear in the 

 plant body, not matched by anything in any known lower form. It is 

 not to be imagined that the whole organization is new that the 

 break in the series is absolute. The nature of the cells upon which 

 the whole character of all vegetable life depends is always the same, 

 and certain reproductive processes are always essentially the same. 

 By the interruption of the series, we mean that in considering the ori- 

 gin of certain plants we are unable to find anything which we can 

 regard as their near ancestry in the lower grades. This is the con- 

 dition in the Liverworts. We may suppose they sprung from an 

 algal stock ; for the plant body is an expanded thallus, the habitat is 

 often damp earth or even water, and reproduction is brought about 

 through fertilization of an egg cell by antherozoids, as in many Algae. 

 But there is nothing by which we can fix the Liverworts as near rela- 

 tives of any particular one of the existing algal groups. 1 



464. Marchantia (Fig. 334), one of the commonest of 

 the Liverworts, is found growing prostrate upon the 

 ground in damp situations. The ordinary length is an 

 inch or two. The thallus forks frequently, and the 

 branches grow forward while the oldest portion of the 

 thalbis continually dies away ; so that finally the branches 



1 By some authorities the Liverworts have been regarded as related 

 to the Stoneworts ( Characece) or the like ; by others to be descendants of 

 Algse resembling Coleochsete, the Water Shield. 



