198 CBYPTOGAMS 



LIVERWORTS AND MOSSES (BRYOPHYTES) 



462. The account of Chloropliyllous 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 

 Algfe. 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 Algte several seeming lines of 

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

 discerneil; 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 o£ structuie. Tn the grand series begin- 

 ning with unicellular Alg?e and ending with Flowering Plants, many 

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

 plant bod}', not matched by anything in any known lower form. It is 

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

 Ijreak in the series is absolute. The nature of tlie 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 o£ certain plants we are unable to tind an^^thiiig which we can 

 regard as their near ancestr}' in the lower grades. This is the con- 

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

 algal stock ; foi- tlie plant body is an expanded thallus, the habitat is 

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

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

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

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



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

 the Liverworts, is found g-i-o:ving prostrate ujwn the 

 ground in damp situations. The ordinary lengtli is an 

 inch or two. The thallus forks frequently, and the 

 branches grow forward while the oldest portion of the 

 tlialbis continually dies away ; so that finally tlie branches 



1 By siirne antliorilies the Liverworts have been regarded as related 

 (0 the Siuiieworts (Chnracen:) or tlic like ; by others lo be descendants of 

 Alg;e rcscmbUng Coleochiete, the Water Shield. 



