MARYLAND WEATHEK SERVICE 169 



it, on account of the easy distribution of these by wind. But Maple 

 seedlings cannot endure strong insolation, so that Sweet Gum and 

 the more slowly distributed trees generally make their appearance. 

 On high ground no tracts were observed which were devoid of pine, 

 but it is probable that in such a case reforestation would be slow, 

 and that oaks would form the prevailing growth, beginning with the 

 most xerophytic species such as Spanish Oak and Post Oak. 



It remains to be considered what is to be regarded as the climax 

 forest formation of the region. It has been shown by Cowles* that 

 extreme conditions such as xerophytic or the opposite tend to be- 

 come more and more mesophytic. Extreme conditions are the sign 

 of a young topography, while the mesophytic condition denotes that 

 processes such as base-levelling have gone on for an extended period, 

 leading to a comparatively stable condition of the flora which may 

 be styled the climax flora for that region. Thus in Washington 

 and Oregon a mesophytic coniferous forest prevails, while in the 

 north-eastern states Maple-Beech forests are found in the most 

 mesophytic situations. The same author offers good evidence for 

 the view that the Maple-Beech formation succeeds the Oak-Hickory 

 formation. It is proper to inquire, therefore, whether the Oak- 

 Hickory formation of our District gives evidence of being replaced 

 by some other, for instance, one containing Maple or Beech. My 

 observations indicate that this is improbable for three reasons. (1) 

 The maple in the district under study is Acer rubrurn, while that 

 in the northern Maple-Beech forests is Acer saccharum. The former 

 is a tree of low ground, and only rarely spreads up the slopes into 

 the oak stands. (2) If on the uplands maple and beech were suc- 

 ceeding the oaks, there should be found areas with a pronounced 

 undergrowth of Acer rubrum and Fagus americana; such areas have 

 not been observed. If the uplands should ever become sufficiently 

 mesophytic to support these that time will be far into the future. 

 (3) Observations as to the nature of the primeval forest of this 

 region do not indicate that this consisted of a Maple-Beech com- 

 bination. The oldest tracts of upland forest found in the district 



*Cowles, H. C. The plant societies of Chicago and vicinity. Botanical 

 Gazette, vol. xxxi, 1901; pp. 73-108, 145-182. 



