208 Pub. Puget Sound Biol. Sta. Vol. 2, No. 46 



The advance of bogs on shallow ponds 



Still another type of bog development is that in which Sphagnum 

 grows submersed and thus encroaches directly upon the open water of 

 shallow pools and ponds without the direct aid of other plants. This has 

 been found frequently where the water was 45 cm. (18 inches) or less in 

 depth. It has been seen by the writer in the following places: Mt. 

 Rainier; upper valley of north folk of Skykomish river; Yakutat, 

 Alaska; Carlisle, Washington. This type of bog advance is often seen, 

 too, in pools within a large bog. Such instances have been observed in 

 Henry bog north of Seattle and in a bog near Covington, Washington. 

 It is a factor also in the gradual encroachment of the later stages of 

 bogs upon the marginal ditch, as is illustrated in a bog near Seabeck, 

 Washington. 



Puget Sound bogs have, then, three ways of advancing upon open 

 water. The first is by the aid of the woody plants that characterize the 

 later stage of the bog itself, so that the mature bog stage advances fully 

 organized, without outside aid. In this case the development stage of 

 the bog is omitted. The second is by the advance of Sphagnum upon 

 herbaceous plants that are not characteristic of the mature bog stage at 

 all, but function in connection with bogs as pioneers onl3^ In this case 

 the bog later develops upon the Sphagnum that has grown upon these 

 herbs. The third method is by the growth of Sphagnum in water, with- 

 out the aid or support of other plants. In this case the bog develops upon 

 the moss when it has grown until the combined bulk of decaying material 

 and living material comes above the surface of the water. 



Floating mats 



It seems quite possible that bogs sometimes form the later succession 

 on free-floating mats of vegetation, but no definite evidence of this was 

 found. Several patches of Sphagnum bog, unconnected with the shore, 

 were found near the extreme southeast side of Mud lake. There were 

 numerous floating mats of other vegetation around them. The insecurity 

 of the footing on many portions of these small bog areas seemed to sug- 

 gest that they might be a later succession on these floating mats, but no 

 intermediate stages were found to establish evidence that this was the 

 case. The lake was drained before time could be found for a detailed 

 study of the situation. 



Species of sphagnum 



The writer has not yet made a sufficient examination of the part played 

 by the various species of Sphagnum in the different types of bog develop- 



