344 



GENERAL MORPHOLOGY OF PLANTS 



spores escape. The wall cells of the capsule contain chlorophyll, 

 and stomates are present in the surface layer. It is thus able to 



make its own carbohydrate 

 food, but is dependent on the 

 thallus for its water and min- 

 eral food. It is thus more 

 highly developed and special- 

 ized than iri the other liver- 

 worts. For this reason the 

 horned liverworts are by some 

 placed in a separate class, An- 

 thocerotes. 



496. Comparative review 

 of the liverworts. The 

 thallus, or plant body, of the 

 liverworts on which the sex- 

 ual organs are borne pre- 

 sents two forms. First, the 

 thallose forms in which the 

 plant body is simply a green, 

 leaf-like or strap-shaped 

 structure of very different 

 form in different genera. 

 Second, the foliose forms 

 in which the thallus is more 

 specialized, being differen- 

 tiated into a slender axis with thin, leaf-like expansions. The 

 liverworts are nearly all land forms, adapted to growing on soil 

 and rocks in wet or moist situations, or on logs or tree trunks, 

 some of the latter being adapted to resist dessication in dry sea- 

 sons. The sperm case does not show much advance over that of 

 some of the higher algae, but it is a more massive structure, and 

 the sperms are quite different and more highly specialized in 

 form. The egg case shows a great advance in structure com- 

 pared with the egg case of the algae, being a multicellular organ, 

 flask-shaped in form. The greatest advance over the algas is 



Fig. 306- 



Anthoceros gracilis. A, several gametophytes, 

 on which sporangiahave developed :B, an enlarged 

 sporogonium, showing its elongated character and 

 dehiscence by two valves, leaving exposed the 

 slender columella on the surface of which are the 

 spores; C, D, E, F, elaters of various forms; 

 G, spores. (After Schiffner.) 



