124 Minnesota Plant Life. 



each alternate generation in the life-history is made up of sim- 

 ilar organisms, while the generations between, although similar 

 to each other, are, in structure, entirely dissimilar to the alter- 

 nating generations. 



The life-history of a liverwort or moss is briefly as follows: 

 Inside the capsules those little urns which rise on their slender 

 stalks above a moss-tuft large numbers of spore-cells are 

 produced, in little spherical sacs, four spores in each sac. The 

 sacs lie loosely in the interior of the developing urn. When the 

 urn is ripe the sacs will have all dissolved, the spores will have 

 separated from each other and in the form of a fine powder lie 

 loose and dry within the urn. In mosses, the urn in most in- 

 stances has a lid which is thrown off and then the spores are free 

 to sift out over the neck and are carried away to places favor- 

 able for their germination. The variety of ways in which mosses 

 and liverworts arrange to scatter their spores at the most ap- 

 propriate times for their well-being need not here be discussed, 

 but later will be given some attention. 



When one of the spores has found a place where the moisture 

 is sufficient for its growth its wall breaks and almost always a 

 green cell is protruded. In a few liverworts the spores divide 

 internally into a little group of cells before their walls break, but 

 in most species this is not common. The green cell grows and 

 divides, building either a little flat plate of cells, reminding one 

 of the flat, fresh-water-algae, or a branching thread, reminding 

 one of some of the thread-algae. In any case not all of the 

 plant-body of this young moss or liverwort is green. Some 

 colorless threads are produced which serve as root-hairs for ab- 

 sorption and attachment. Such an immature moss or liverwort 

 plant is called the first-stage of the moss. The first-stage may 

 continue for some time and in a few little mosses it forms a 

 green mass of creeping threads which covers on clay banks a 

 considerable area. Usually, however, the first stage in both 

 mosses and liverworts is comparatively small and transitory. In 

 peat mosses it makes a difference in the structure of the first- 

 stage whether the spores germinate in water or on land. When 

 they germinate in water the first-stage has been known to take 

 the form of a branching thread, but when they germinate 011 

 land, the first stage becomes a flattened plant-body half an inch 

 or more in length, and one layer of cells in thickness. 



