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



since the bog has encroached more rapidly in some places than in others. 

 The water is 1.8 m. (6 feet) or more in depth at the very margin of the 

 lake. This was tested by standing on the margin of the Sphagnum (a 

 none too secure footing in many cases )and thrusting a pole down. Where 

 bottom was reached it was, of course, of very soft material into which 

 the pole could be pushed with little effort. In some places it was found 

 that the surface of the bog projected out over the lake so that the pole 

 could be thrust backward under the mat of vegetation on which the 

 observer was standing. 



Labrador tea, swamp laurel and cranberry were all observed as pio- 

 neers in the advance of Sphagnum on this lake. The first two are naturally 

 more effective than the last on account of their stronger stems. Sometimes 

 all three were found together, sometimes one alone, and in other places two 

 of them together provided the means for the advance of the Sphagnum. 

 All possible combinations of the three were found. The stems of these 

 shrubs grow out into the lake, and their growing tips rise above the surface. 

 Sphagnum keeps growing out on the surface of these and weighting them 

 down. To a certain extent the growth of these tips keeps pace with the 

 weighting down of the stems by the growing Sphagnum, and the woody 

 stems of these species thus becomes deeply imbedded in the bog. The 

 lake is finally filled up to the surface mat largely by organic matter. A 

 good deal of this undoubtedly drops from the bottom of the mat while the 

 continued growth of vegetation on top replaces the material thus lost. To 

 what extent plankton material may contribute to the filling of this lake 

 has not been investigated. 



Another illustration of the advance of a bog on a lake is found near 

 Sunnydale just south of Seattle. This lake is considerably smaller than 

 Crystal lake, and is much shallower at the margin. In the main, the 

 bottom of this lake slopes very gently down from the surface of the 

 bog. No place was found where the water was more than 30 cm. (1 foot) 

 deep at the edge of the bog. It has a zone of water lily {Nympliaea poly- 

 sepala) and purple marshlocks {Comarum pahisii-e) around it, and these 

 are largely the forerunners of the bog. The water lily seems to function 

 largely by filling the lake margin with organic matter. It does not act as 

 a direct support for Sphagnum. Purple marshlocks on the other hand, 

 functions in the shallow water here somewhat as the woody bog plants 

 do in Crystal lake. Its stems form a rather dense mat beneath the water, 

 while its leaves rise above the surface. This mat forms the support for 

 the advancing moss. Labrador tea, swamp laurel and cranberry are found 

 to a limited extent as bog pioneers, but their role is a minor one. 



A bog borders the south side of Kitsap lake in Kitsajj county, but 

 does not seem to be making much progress upon it, since large coniferous 



