1922] Forest Types 197 



(6) Frothingham, Journal of Forestry 19:1. 1921. 



(7) Mechanical condition is the basis for the classification of soil types 

 employed by the Bureau of Soils of the Department of Agriculture ; while the 

 moisture content, and the number of times that the critical moisture period is 

 reached (Briggs and Schantz, the wilting coefficient) are determined by (1) 

 humus content and granulation, (2) depth of water table, (3) transpiration 

 factors of wind and insolation, the precipitation being the same; and these are 

 controlling factors in determining site. 



(8) Kearney, Science 12:841. 1900. Noted particularly also by Shreve, 

 Vegetation of a Desert Mountain, 97. 1915. The result of differences in inso- 

 lation is noticeable to a marked degree in the southern portion of Walker County 

 and in Jasper County, Alabama, along the southern edge of the Alabama National 

 Forest. Here on the uplands are typical forests of longleaf pine while in the 

 deep gorges of the streams penetrated by direct sunlight only during a few hours 

 each day may be found fragments of hemlock — black birch type; and the yellow 

 poplar — cucumber — beech — black birch — northern red oak mixture. To a less 

 extent this is also noticeable in the deep hollows which indent the bluff formation 

 along the Mississippi River in its most dissected phases. 



(9) Contrary to general opinion, many of the surface soils derived from 

 limestones, in cases where the unaltered limestone is at a great depth, are not 

 only not neutral but even acid. This is due to the fact that the so-called lime- 

 stone soils, produced from the weathering of impure limestone, are residuals, 

 consisting of the less soluble, chiefly silicious materials. The more rapid is 

 erosion the thinner, as a rule, is the residual blanket permitting the roots of 

 more plants to come in contact with the calcareous elements in the unleached 

 limestone. Many of the residual soils in the Appalachians from the Silurian and 

 Cambrian limestones, consequently, are acid and support stands of plants asso- 

 ciated with acid soils. 



(10) North Carolina Pine, Bull. 24, N. C. Geo. Survey, p. 57. 1915. 



(11) In the superior stand or sun stand certain species (like yellow poplar) 

 may be largely intolerant of shade throughout their entire life period. Such 

 species produce relatively few suppressed trees in the mature stands. Other 

 species, like beech and white oak, are tolerant for a long period and consequently 

 produce many suppressed specimens; while tolerance of some others, like balsam, 

 progressively declines with age. The leaves of dominant and suppressed trees 

 of the same species, or the sun and shade leaves on dominant trees may be quite 

 different. In the southern red oak and its races the sun leaves are smaller, more 

 divided, and more densely pubescent beneath. In TiJia lieterophylla of Authors 

 the shade leaves are larger, thinner, and often glabrous, having been mistaken for 

 T. glabra, whereas the sun leaves are silvery-white pubescent beneath. The 

 records of the occurrence of T. glabra in the eastern Appalachians are largely 

 based on collections of such shade leaves. 



(12) Botanical Gazette 34:241, 369. 1903. Unfortunately the value of 

 these articles is marred by a number of errors in the determination of very com- 



