[january BOTANICAL GAZETTE 48 



keep the trees down; but if the patch be undisturbed, the sapling 

 growth can replace blackberry in a few years (pin cherry in 3 or 4 

 years). The thorn species are widely sown by animals that eat 

 the fruits, so their armament serves rather for climbing and indivi- 

 dual protection than for keeping out animals. Erigeron canadensis 

 L. is the commonest holdover from the fireweed flora. Forerunner 

 saplings are also very usually present. Thus this stage serves as 

 transition where herb and tree meet. It can hold a vicinity far 

 longer than the fireweed society. 



Fern society. — Pteris aquilina L. occurs with some grass on 

 xerarch areas. Because of its flat-topped habit and proneness to 

 form a pure stand of fronds of equal age and height, this fern forms a 

 synfolium at from 40-80 cm. from the ground, the distance varying 

 with age. Bracken is commonly associated with grass sod, coming 

 in after continuous destructive interference in the drier hilly upland 

 and exposed shore hills. Aspen often is found with it, both entering 

 particularly after fire (12). Myrica asplcnifolia societies of farther 

 south (Little Manistee to Brethren) appear to be equivalent. 



Milkweed society. — The species is not native of the region. 

 Asclepias syriaca L., while common as a weed, and found in all sorts 

 of societies, also forms a persistent, ubiquitous, and actively invad- 

 ing society of its own on drier upland and lowland areas. Like 

 Pteris, it is often associated with grass turf, possibly because of the 

 natural openness of the two societies. It probably enters after 

 more severe and continuous interference than the bracken can 

 endure. Because of its underground rhizome, xerophytic structure, 

 tremendous reproduction, and efficient seed dispersal, it can main- 

 tain itself after continued cutting and even plowing. It probably 

 would precede sumac in reclamation of unused upland pastures, 

 and is prominent where interference (and turf?) prevents later 

 successional stages in pasture and grassy upland. 



Sumac society. — These species are probably native here. Rhus 

 typhina L. and R. glabra L. occur in upland pastures, along roads, 

 and in clearings, being primarily a bordering association (thus later 

 than milkweed) , occurring more often on closed (and especially clay) 

 soil. It forms a stand 1-2 m. high, much opener than the milkweed, 

 and being taller permits more herbage. Along roads it is often 



