i 9 2o] TAYLOR— SUCCESSION OF MOSSES 489 



low growing seed plants which nearly smother out the mosses. 

 The increase in shade and possibly other conditions in the late 

 shrub stage and early tree association apparently are unfavorable 

 for most of the old herbaceous species, and new ones have not 

 taken their places, so that there are large areas unoccupied by such 

 ground vegetation. As in the pine dune, so also here we may have 

 toxicity produced by decay of conifer needles. This probably does 

 not greatly retard the moss development, although it may account 

 in part for the change in species. With herbaceous plants, on the 

 other hand, it may result in almost total elimination. The rapid 

 increase of quantity and number of species of moss in the early tree 

 association, therefore, is directly related to these environmental 

 conditions. The greater shade and lower temperature are both 

 more favorable to moss growth, and added to these is the lack of 

 competition with other plants. 



As the tamaracks are replaced by deciduous trees, the mosses 

 give place to herbaceous seed plants. The chemical condition of 

 the subsoil changes, more humus accumulates, moisture and 

 humidity decrease. The mosses now are crowded out of their 

 former locations until, with few exceptions, they persist only on 

 sticks, logs, and tree bases, and we find in their place many ferns 

 and seed plants. Competition seems to be the great cause of the 

 elimination. Some general conclusions regarding the pond and 

 lake successions of mosses are as follows. 



Very few mosses appear in the pannes, but those which are 

 present are coarse and aid in filling up the depressions. The 

 lagoons are favorable habitats for floating species, while other 

 mosses are abundant along the margin. Both produce material 

 which is added to the muck on the bottom and which provides 

 nourishment for other plants. Still other species assist in the 

 formation of floating islands. In the bogs a few species of semi- 

 aquatic mosses appear in the early fen stage in considerable quan- 

 tities. There is a slight decrease in quantity in the shrub stage. 

 A marked increase in quantity and number of species is evident in 

 the early tamarack association and continues until the tamaracks 

 are replaced by deciduous trees, making the tamarack the domi- 

 nant moss association. In the later deciduous association there is 



