Jennings : A Botanical Survey of Presque Isle. 357 



Salix discolor. 

 Principal Species. — 



Solidago canadensis, Aster ericoides. 



Secondary Species. — 



Scleria i>erticillata, Lininn niediinn, 



N'ostoc S]). 



The Solidago canadensis aspect is very conspicuous in the fall, just 

 as in the Alyrica thicket-formation on the sand-plain. There is much 

 similarity, in fact, between these two thicket-formations, but in their 

 manner of origin they are quite distinct, and the willows do not enter 

 into the structure of the thicket on the sand-plain. 



The beginning of the Myrica-Salix thicket-formation is best ex- 

 emplified in the "swale " which marks the former extent of a lagoon, 

 of which Lagoon D is the remnant (see Plate XLV). This swampy area 

 averages about three rods in width and extends from Lagoon D towards 

 the Fog Whistle for a distance of about one-eighth of a mile. The 

 area is but a little lower than the sand-plain adjacent and the habitat 

 now affords a beautiful example of a mature Scirpus americanus con- 

 socies of the Typha-Scirpns formation. This formation, however, is 

 bordered by a Sabbatia-Linmn zone, which is being rapidly supplanted 

 by the Myrica-Salix zone. The pioneers of the shrub zone are Myrica, 

 while the two willows and the Aster are just appearing. 



Stage E. — Lagoons E, Ea, F, and Fa. 



(^z) Potainogeton Formation, 



(/^) NytnphcBa Formation, 



(r) Scirpns-Typha Formation, 



{d) Cladiiim-Calamagrostis Formation, 



((?) Alyrica- Salix Formation, 



(/) Populus-Salix Formation. 



Stage E is exemplified around Lagoons E, F, and Fa, which were 

 apparently segregated from the lake at about the same time, being 

 nearly in line with each other abreast and being very similar in their 

 vegetation (see Plates XLVI and XLVII). 



The Potamogeton Formation. 



The Potamogeton formation here is becoming somewhat more re- 

 stricted but at the same time it is better developed and is more 

 clearly defined from the zones surrounding it. It occupies the deeper 

 water of the lagoons, shallowing out to a depth of about five feet. 



