38 Rhodora [MARCH 
glaucophylla, could not be found, but its soils are no doubt similar in 
reaction. 
In the most exposed places of all, near the summits of the moun- 
tains, the soil consists chiefly of frost-broken rock fragments, and even 
these Ericaceae are unable to gain much foothold. Rhododendron 
lapponicum and Diapensia lapponica are typically developed in this 
sort of situation, along with scattered colonies of the other species. 
The crumbling rock itself, where as free as possible from organic 
matter, ranges in reaction from subacid to neutral, the acidity being 
apparently due to the presence of minute lichens, etc. ; but on testing 
the material at the roots of the plants mentioned, a mediacid reaction 
was almost invariably obtained, because of the presence of humus 
mixed with the rock fragments. Seedlings of these plants were oc- 
casionally found in material of lower acidity, but the reaction around 
them is never less than subacid. 
The distribution of plants of other groups with reference to the 
soil acidity is also a matter of interest. Among ferns, the absence of 
the usual rock-growing species, such as the Woodsias and true Asplen- 
iums, is a striking feature, the soils apparently being too acid for these. 
Three specimens of ferns were noted above the tree-line, in mediacid 
alpine peat on rocky ledges: Phegopteris polypodioides (Phegopteris), 
Aspidium (Dryopteris) spinulosum, Asplenium Filix-femina (Athyrium 
angustum). These ascend to very high elevations, the last reaching 
practically to the summit of Mt. Washington itself (1917 meters), al- 
though all are considerably dwarfed. Lycopodium Selago var. appres- 
sum and L. annotinum var. pungens appear in the most exposed situa- 
tions, the soils being likewise mediacid or rarely subacid. 
Of flowering plants other than Ericaceae, the following are note- 
worthy. In damp soils of mediacid reactions grow Streptopus roseus, 
Coptis trifolia, Trientalis americana, and Lonicera caerulea var. villosa. 
In drier, though not the most exposed places, grow also Maianthemum 
canadense, Clintonia borealis, and Cornus canadensis. In the bare 
rocky ground, where Diapensia flourishes, occur Salix Uva-ursi, 
Arenaria groenlandica, Stellaria borealis, Potentilla tridentata and 
Geum (Sieversia) Peckii; the Stellaria and a grass, Poa laxa, being the 
only plants observed at the actual summit of Mt. Washington. The 
soils of all these species proved to be normally mediacid in reaction. 
Soils of minimacid reaction were found to occur on the White Moun- 
tains only in springy places. Ericaceous plants were in no case ob- 
