52 Oekologie. — Geographie. 



encroachment of one zone of Vegetation after another the ponds 

 are ultimately transformed into swamps and these become 

 mesophytic prairies or forests. 3) Uplands, whether of rock^ 

 sand, or clay, have at first an intensely xerophytic flora. On 

 clay the stages of development are more rapid than on sand 

 or rock, but in all cases alike a mesophytic forest ultimately 

 appears. 4) Lake bluffs represent retrogressive activities, erosion 

 increasing the xerophytic conditions. If erosion ceases, 

 however, one type of Vegetation rapidly succeeds another, 

 culminating in the mesophytic forest. 5) As shown in a prece- 

 ding paper, dune Vegetation passes through a number of stages, 

 especially cottonwoods, pines, and oaks, culminating in the 

 typical mesophytic forest of beech and maple. 



H. C. Cowles. 



Collier, A. C, Notes on the Vegetation. (Brooks, A. H. 



A reconnaissance of the Cape Nome and adjacent gold fields 



of Seward Peninsula, Alaska, in 1900. p. 164 — 174. Washington, 



U-S., Geological Survey. 1901.) 



Ten lichens, three ferns, and 67 authophytes are recorded, with 

 brief notes on their distribution, economie value, etc. The Vegetation is 

 stated to be of an arctic character, though spruce trees (tentatively 

 referred to Picea Canadensis) a foot in diameter and 50 ft. high were 

 measured on Ninkluk River. Trelease. 



Whitford, H. N., The genetic development of the 

 forests of Northern Michigan; a study in physio- 

 graphic ecology. (Contributions from the Hüll Botanical 

 Laboratory. XXVII. The Botanical Gazette. Vol. XXXI. 

 1901. p. 289—325. With text figures.) 



Three sets of factors control the presence or absence of 

 trees, viz., climatic, ecological, and historical. The climatic 

 factors of heat and temperature bring about the great plant 

 formations such as forest and prairie. The ecological factors, 

 due primarily to topographic diversity, cause the plant society 

 condition. However the topography is constantly changing so 

 there is a readjustment of plant societies to meet the new 

 conditions. 



Beginning with areas where Vegetation is entirely absent, 

 the successive societies are traced through four series of topo- 

 graphic situations, viz., sand, clay, rock, and swamps. In the 

 first three situations there is a passage from the xerophytic 

 heath, through the coniferous forest to the mesophytic deci- 

 duous forest. In the swamp the successive plant zones from 

 the margin to the center encroach upon each other and fill up 

 until the water level is far enough below the surface to allow, 

 first a coniferous growth of tamarack and spruce, and then the 

 deciduous forest of maple and beech. Clearing societies show 

 a similar succession, though here fire weed and birch-poplar 

 growths usually precede the maple-beech combination. In all 



