An Ecological Study of Buckeye Lake. 59 



many invaders from without, some of these remain and so from 

 year to year the association receives additions to its flora. This 

 is partially due to the position being a marginal one. In this it 

 resembles the marsh but the greater shade afforded seedlings by 

 the shrubs seems to protect them from excessive transpiration. 

 Winds carry seeds from surrounding areas, the marginal thicket 

 serves as a wind break and many of the seeds do not reach the 

 central zone. Other seeds are transported by water currents 

 and become lodged on the peat shelf among the exposed roots 

 at the margin or may be washed farther in. The trees and 

 shrubs offer a resting place for the birds ; and the fruits and 

 seeds they carry are dropped among them. The seedlings of 

 Quercus palustris, O. imbricaria and Fagus americana can only 

 be accounted for in this way. 



The position of the thicket is unique in that it lies between 

 the marsh and meadow. In many bogs the meadow is wanting; 

 where it is present, it is generally a sedge-grass meadow and in- 

 tervenes between the shore vegetation and shrub zone. The 

 normal order of succession seems to be : 



Floating aquatics. 



Fixed aquatics, submerged or with floating leaves. 



Marsh. 



Meadow. 



Low shrub or heath. 



Thicket. 



Forest. 



This succession has not developed uniformly on Cranberry 

 bog, for the thicket has invaded the marsh zone on the one side 

 and the bog-meadow on the other; so that not only is the inner 

 margin of the thicket quite irregular, but detached individuals 

 and masses of shrubs have pushed into the meadow and are 

 scattered all thru it. (Fig. 23.) 



It is also difficult to draw a line of demarcation between the 

 bog-thicket composed of shrubs and the bog-forest or even to, 

 distinguish a transition zone between them. 



