LOWER LAND PLANTS 



161 



urn liverwort gametophytes, 

 sporophytes minute 



leafy liverworts, 2 or 3 



rows of leaves^ often with 



lobed leaves, leaves without midveins 



ribbed liverworts, no reproductive 

 branches^ sex organs inconspicuous 

 along midline, hence sporophyte not 

 terminal 



Figure 10.4 Liverwort types exclusive of pore liverworts, about natural size except for the two 

 urn liverworts. 



leaves (see Figures 11.3 and 11.4) regularly alternate 

 and sessile (rarely opposite), flattened, entirely with- 

 out midribs (a very few with elongate cells giving a 

 semblance of a midrib), and variously shaped; lateral 

 leaves entire, notched, two-cleft, two-lobed, or more 

 complexly cleft, lobed, or divided; when leaves are 

 largely separated into two parts, one part often is 

 smaller and folded under the larger part, or under- 

 folded part is larger and plant appears to have four 

 leaf rows; underleaves may be absent or may be as 

 large as lateral leaves; a few aquatic species have 

 leaves or leaf parts bladder-like; leaves with or with- 

 out gemmae cups; if present, gemmae cups usually 

 are near tips of young leaves; gametophytes with male 

 and female organs on one or separate plants. Male 

 sex organs nearly always in the axil (angle formed by 

 leaf upon stem) of lateral leaves, some on the under- 

 leaves; sex-organ-bearing leaves generally organized 

 into a cone-like structure. Female sex organs are 

 normally at the end of the stem in the region of 

 growth, also, on growth region of a normal branch or 



on a special branch; sex-organ-bearing leaves form a 

 bud-like structure resembling that of early developing 

 leaves. 



Reproduction: asexual, drought may kill all plant 

 parts except the growth regions at the ends of stems; 

 gemmae are produced in some forms; sexual, generally 

 as in Anthocerotae. 



SPOROPH'.TE 



Structure: consisting of a capsule with or without a 

 stalk and foot. In the capsule spores normally mature 

 at the same time. Then the capsule opens along two 

 or more valves, usually four. The stalk and foot grow 

 rapidly but do not develop until after the spores ma- 

 ture. The end of stalk and foot growih is followed by 

 immediate capsule opening (typically into petal-like 

 segments) and shedding of spores. 



Most liverworts inhabit moist, generally disturbed 

 areas. They almost encompass our globe, ranging 

 from frigid to tropical areas. In the Arctic, there are 



