LIVERWORTS. 



237 



There is so much moisture in these little pockets of the under 

 side of the leaf that minute animals have found them good places 

 to live in, and one frequently discovers them in this retreat. 

 There is here also a third row of poorly developed leaves on the 

 under side of the stem. 



498. Porella. Growing in similar situations is the plant known as 



porella. Sometimes there are a few plants 

 in a group, and at other times large mats 

 occur on the bark of a trunk. This plant, 

 porella, also has closely overlapping leaves 

 in rows on opposite sides of the stem, and 

 the lower margin of each 

 under somewhat as 

 in frullania, though 

 the pocket is not so 

 well formed. 



The larger plants 

 are female, that is 

 they bear archego- 

 nia, while the male 

 plants, those which 

 bear antfieridia, are 

 smaller and the an- 

 theridia are borne 

 on small lateral 

 branches. The an- 

 theridia are borne 

 in the axils of the 

 leaves. Others of 

 the leafy-stemmed 

 liverworts live in 

 damp situations. 

 Some of these, as 

 Cephalozia, grow on damp rotten logs. Cephalozia is much more delicate, 

 and the leaves are farther apart. It could not live in such dry situations 

 where the frullania is sometimes found. If possible the two plants should be 

 compared in order to see the adaptation in the structure and form to their 

 environment. 



499. Sporogonium of a foliose liverwort. The sporogonium 

 of the leafy-stemmed liverworts is well represented by that of 

 several genera. We may take for this study the one illustrated 



I'ig. 270. 



Thallus of a thalloid liverwort (blasia) showing lobed 

 margin of the frond, intermediate between thalloid and 

 foliose plant. 



