1920.] NATURAL SCIENCES OF PHILADELPHIA 89 



showed subacid to mediacid reaction. The control of the distribul 

 tion of Ericaceae by the soil reaction is here so evident as to require 

 no further comment. 



No other locahties in the mountain region need special descrip- 

 tion, the acidities of the soils of Ericaceae observed there being 

 included below, but the data which have been obtained on a few 

 plants of other families than Ericaceae may be added here. The 

 following were found to be limited to mediacid or occasionally sub- 

 acid soils: Clintonia borealis, Trillium erythrocarjnim, Tiarella cordi- 

 folia, DaUharda repens, Waldsteinia fragarioides, Oxalis acetosella, 

 Poll/gala pa ucif olia, a.nd Trientalis borealis. In circumneutral soils, 

 rarely ranging to subacid, characteristic plants are: Cryptogramma 

 stelleri (Pellaea gracilis), Filix fragilis, F. bulbifera, Camptosorus 

 rhizophyllus, Allium tricoccum, Aquilegia canadensis, and Castilleja 

 coccinea. Wide range of reaction is shown by Taxus canadensis, 

 Trillium erectum, Clematis verticillaris, Hepatica acutiloba, Viola 

 pedata, etc. Finally it may be noted that Phlox subulata, while its 

 acidity range is wide, shows more or less correlation of flower-color 

 with soil reaction, in that the deep rose-violet flowered plants are 

 usually found to grow in soil of lower acidity than those with pale 

 rose or white flowers. There are, of course, cases in which both 

 grow in close association, and where this relation does not hold, but 

 in general it seems to be fairly definite. 



Valleys in East Central Counties of Pennsylvania 



The Lehigh-Lebanon valley of eastern Pennsylvania is largely 

 underlain by limestone rocks, but at many places there is a thin 

 layer of glacial drift over the limestone. The soil reactions assoc- 

 iated with such a geological relationship and the resulting distri- 

 bution of Ericaceae are matters of considerable interest. Tests have 

 shown that the soil of unprotected limestone rock is normally mini- 

 malkaline or neutral in reaction; but that where the glacial drift 

 occurs, upland peat tends to develop, often reaching a minimacid 

 and occasionally even as high as subacid reaction. Woods in which 

 many acid soil plants grow can develop in such drift-covered places, 

 but where these woods are cut over and the acid upland peat material 

 is given a chance to decompose, the acidity may decrease decidedly. 

 No doubt under such circumstances those species which require the 

 most acid conditions die out rapidly, while those which can adapt 

 themselves to a less degree of acidity persist for some time, even to 

 the point where the reaction goes down to the neutral point. 



