142 Minnesota Plant Life, 



move them without breaking their stems in pieces. In such 

 liverworts it is not the stem of an egg-organ-bearing branch 

 that elongates to assist the spores in their dissemination but the 

 true stalk of the capsule, showing that the plant has developed 

 in the spore-producing generation itself the structures requisite 

 for assistance in spore-distribution. Unlike the horned liver- 

 worts, the capsules in this group, which are commonly spherical 

 in form and considerably smaller, do not need and accordingly 

 do not develop a central column of supporting tissue, but the 

 entire cavity of the capsule is occupied by the spores and elaters. 



A peculiar thing about the vegetative plant in many of the 

 higher liverworts is the production of two lobes in the leaf, one 

 of which is turned under the other. The one turned under and 

 facing the lower side of the prostrate stem is sometimes modi- 

 fied into a little pitcher and is then called a water-pocket because 

 it serves to retain moisture that in drouths the plant might find 

 serviceable. In such little water-pockets on the under sides of 

 certain liverwort leaves tiny worms often make their homes. 

 It is difficult to see how they can be of any great advantage to 

 the liverwort, but they are so invariably present in some species 

 that there must be a partnership arrangement between the plant 

 and the worms which dwell upon it. In the water-pockets, too, 

 there are often found colonies of simple algae which avail them- 

 selves of the small drop of water to grow and develop. In 

 certain exotic species the water-pocket becomes a trap which 

 catches small insects, as bladderworts do. 



A very great variety of leaf-forms characterizes the leafy 

 liverworts. Sometimes the leaves are flat and scale-like, hence 

 the name of scale-mosses which is commonly applied to plants 

 of this group. Again the leaves are slender or dissected into 

 fine teeth, and they may even become modified into little 

 branching green bristles, which look quite unlike an ordinary 

 leaf. In the tropics such leafy liverworts dispose themselves 

 upon the leaves of larger flowering plants and often make char- 

 acteristic patches of vegetation where there is an abundance of 

 moisture. The greater number of kinds in Minnesota display 

 themselves upon the bark or upon damp soil along with mosses 

 from which they are not at first very easy to distinguish. They 



