ORIGIN OF LIVERWOETS 127 



of the breath. Similar movements take place in Nature, 

 while the elaters are amongst the spores; they are, doubt- 

 less, a device for spore- dispersal. Both elaters and 

 spores are discharged together from the ruptured cap- 

 sules. The structure of the sporogonium is illustrated 

 in Plate IV., Fig. 8; and in Fig. 9 we have a drawing of 

 an extended elater as seen under the microscope. The 

 spores, on germination, give rise to new gametophytes. 



In giving the outline of the structure and development 

 of Merchantia 'polymorpha, we have stated only the 

 salient features, and have omitted several minor details ; 

 suflS.cient, however, has been said to indicate that this 

 plant, apparently so humble, and so frequently ignored, 

 has really quite a complicated structure, and is most 

 ingeniously adapted to the conditions in which it thrives. 

 In the floating Riccia nutans we can imagine an Alga 

 with flattened thallus adapted to floating conditions, 

 and with modified reproductive organs. The same 

 plant stranded on mud has power to adapt itself to the 

 change, and then displays decidedly amphibian charac- 

 ters. In Marchantia we have a more decided terrestrial 

 plant, but one that is aquatic in relation to its fertiliza- 

 tion. The great probability is that the Liverworts have 

 descended from Algal ancestors, and that they represent 

 a series of stages whereby plant-life, originally aquatic, 

 has advanced in the conquest of the land. The gemmae 

 of the Liverworts may be regarded as highly modified 

 zoospores, and the male and female elements, particu- 

 larly the ciliated spermatozoids, argue strongly in favour 

 of an aquatic ancestry. 



AnthocerotacecB. — The species distinguished number 

 103. The gametophyte is a simple, irregular, disc- 



