1922] WATERMAN—PLANT COMMUNITIES 17 
pioneer, associated with Artemisia caudata, Calamovilfa longifolia, 
Cirsium Pitcheri, Campanula rotundifolia, Cakile maritima, Lathyrus 
maritima, Prunus pumila, Salix longifolia, S. syrticola, Senecio vul- 
garis, Solidago spp., Aster sp., Zygadenus chlorantha, Hudsonia 
tomentosa, Arctostaphylos uva-ursi, Juniperus communis, and J. hori- 
zonialis. All of these are able to germinate on dune sand, but 
only Ammophila is able to become established in pure sand. The 
others are stunted and soon die, unless their roots come in contact 
with buried plant material, from which apparently they are able 
to obtain the necessary mineral elements. Ammophila and perhaps 
Calamovilfa are the only plants which cover the ground _ thickly 
enough to act as stabilizers. The other herbaceous plants are also 
scattered, and never grow close enough to form a ground cover in 
the moving dune belt. Arctostaphylos and Juniperus horizontalis 
germinate occasionally on the open sand, but it is doubtful whether 
they can stabilize. Whenever they occur in sufficient quantity to 
cover the ground, it is usually by invasion from a patch already 
established. 
Hydrarch.—Juncus balticus and willows are the usual pioneers 
in pannes. Occasionally a local patch of Pinus Banksiana, with 
more or less Thuja occidentalis, Abies balsamea, and Betula alba, forms 
a clump or grove, which may reach the size of several acres and 
spread over small valleys or local patches of level sand. There is 
no evidence of any extensive permanent stabilization by coniferous 
trees in the belt of moving sand next to the lake. They frequently 
occur as narrow strips or tongues between advancing lee slopes. 
The transition from this area to the pine-oak ridges is very marked as 
one crosses the irregular line of crescent-shaped lee slopes and comes 
to the lower rounded ridges, where the force of the wind is much less 
marked and the plants of the pine-oak stage have become estab- 
lished. From this it would appear that the coniferous tree stage 
originates in pannes, but does not really become widespread so as 
to form a forest into which the more mesophytic pines and oaks 
gradually migrate and become dominant, but that the coniferous 
patches are relatively scattered, and their only influence is as 
humus formers and as centers of distribution for certain elements 
of the pine-oak stage. Stabilization, therefore, is due to a diminu- 
