128 PLANT-LIFE 



shaped thallus, each cell being occupied by a single 

 large chloroplast containing a pyrenoid (p. 32); in this 

 respect the cells of the Order differ from those of all other 

 Bryophytes. The archegonia are sunk in the upper 

 surface of the thallus ; the antheridia rise from cells that 

 divide beneath the epidermis, and they remain in 

 cavities below the surface until they are mature. After 

 the archegonia have received the spermatozoids and 

 the egg-cells are fertilized, the adjoining tissue over- 

 arches them. The growing sporogonium eventually 

 ruptures the covering tissue, which then forms a sheath 

 round the foot of the capsule. The sporogonium is a 

 long podlike capsule with a swollen foot. In liberating 

 the spores, the capsule splits longitudinally, exposing 

 a long central strand of sterile tissue — the columella. 

 Elaters occur among the spores. It is remarkable that 

 stomata are found in the walls of the sporogonium, and 

 its cells contain chlorophyll; this indicates capacity for 

 carbon assimilation and an attempt towards indepen- 

 dence of the sporophyte, such as is not shown in other 

 Liverworts. It is probably because of this capacity for 

 self-help that in all the Anthocerotes the sporophyte 

 does not wither so soon as its first spores are ripe; but 

 it continues to grow for a time, and produces a succession 

 of spores. In this Order we have a further illustration 

 of the strange relations of plants highly divergent in 

 character; colonies of the Blue-G-reen Alga Nostoc are 

 always found in intercellular cavities of the thallus. 



Jungermanniacece. — Named after Jungermann, a Ger- 

 man botanist of the seventeenth century. This is by 

 far the largest Order of the Liverworts ; it includes over 

 3,500 species, some of which are thalloid, but most are 



