186 BOTANICAL GAZETTE [ance 
cottonwood dunes are common southward, but rarer north 
ward, since cottonwoods are rarer northward. This is only ont 
of the many cases where ecology helps to interpret physiography. — 
The dune-forming plants are not the only tenants of the — 
beach dunes. Most of the species that grow on the upper beach 
are also frequently present on the dunes. Those of especial 
importance are Artemisia Canadensis (or A. caudata), (nitls 
Pitcheri, Lathyrus maritimus, Euphorbia polygonifolia, and Corispi — 
mum hyssopifolium. By reason of its extensive vegetative prop 
gation, Juncus Balticus littoralis sometimes serves as an obstacle 
to sand-laden winds, and by a limited subsequent growth results | 
in the formation of miniature dunes.  Lithospermum hartum, 
though more characteristic of embryonic heaths and rejuvenated 
dunes, sometimes ventures out upon the beach dunes. It should 
be likewise noted that any of the dune-forming species are likely ; 
to grow on dunes that are formed in the main by others, althougi 
the vegetation of individual embryonic dunes is often composed 
of a single species. | 
Though no plant formation anywhere can have am 
percentage of plants that are entirely independent of 
plants, the beach dunes, nevertheless, have occasional forms the! 
are parasitic, saprophytic, or epiphytic. Various unidentie 
Basidiomycetes have been found in the most open places: ee 
ing their nutriment from buried driftwood. The most 2° 
parasite found was Aphyllon fasciculatum, a plant which aie : 
its nutriment through attachment to the roots of Artemis ( 
Lichens are abundant on the cottonwoods at all places that ee : 
not directly exposed to a fierce sand-blast action. eee 
lichen species in such places are Physcia stellaris, Thelosie” 
concolor, and Placodium Sp. mall 
Interesting beach dunes were seen on the shores of Oe: 
inland lakes, Crystal lake, near Frankfort, and Foun : 
Beaver island. In each case the lakes approach a dune ee 
the shore of Lake Michigan, suggesting the probable a 
the sand; there can be no question, however, but that te 
composing these beach dunes was washed up by ne 
uch large! | 
other 
t lake e 
ways 
