94 PROCEEDINGS OF THE ACADEMY OF [Mai'ch, 



The growing season, or interval between average dates of minimum 

 temperatures of 0° C (32° F.), is about 200 days in length. 



The region around Millsboro is farmed extensively, but the native 

 vegetation is preserved here and there, especially along the banks 

 of streams. The dominant tree is Pinus taeda, and mingled with it 

 are P. serotina, P. echinata, P. rigida, and P. virginiana. Oaks, 

 maples, and gums are the principal deciduous trees. In the swamps 

 occur Chamaecyparis thuyoides and rarely Taxodium distichum. A 

 striking feature of the pine forests is the sparsity of the undergrowth, 

 in which they resemble the southern rather than the New Jersey 

 Pine-barren regions.^ 



The most prominent smaller trees and shrubs include Myrica 

 caroliniensis, Magriolia virginiana, Alnns rugosa and the southern 

 species A. maritima, Ilex opaca, I. glabra, Pyrus (Aronia) arhutifolia, 

 Aralia spinosa, Cornus florida, and some 15 ericaceous plants, divi- 

 sible into two groups: those of mediacid, and those of subacid 

 soil. The mediacid soil species which mostly grow in swamps, are: 

 Clethra alnifolia. Azalea viscosa, Kalmia angustifoha, Euhotrys race- 

 mosa, Xolisma ligustrina, Gaultheria procumhens and Vaccinium 

 corymhosum. The Gaylussacia hrachycera itself grows in dry upland 

 peat with mediacid to high subacid reaction. The species more 

 characteristic of dry subacid soils are: Chimaphila maculata, C. 

 umhellata, Azalea nudiflora, Kahnia latifolia, Epigaea repens, 

 Gaylussacia baccata, and Vaccinium vacillans. 



Mediacid reaction was found to be present practically throughout 

 the swamps, both in the water and the peat, and also in upland 

 peat of the dry hills. On digging down into the sand beneath such 

 upland peat, the acidity was found to decrease markedly, the meas- 

 urements being: Surface, specific acidity 300; 25 centimeters down, 

 100; 50 cm. down, 30; and 100 cm. down, 10. As in the New Jersey 

 Pine-barrens, both natural and artificial depressions often show the 

 lower acidities on their banks, which relation controls to a certain 

 extent the distribution of plants. 



Two plants were observed to grow in this region which are else- 

 where characteristic of circumneutral soils, Asplenimn platyneuron 

 and Aquilegia canadensis. The first appears chiefly in isolated 

 patches in the pine woods, where either because of the presence of 

 bacteria able to decompose the acid constituents of the upland peat, 



^Compare Harper, Bull. Torrey Bot. Club, 37: 426, 1910; Bull. Geogr. Soc. 

 Phila. 16: 14, 1918. 



