180 BOTANICAL GAZETTE [MARCH 
along Lake Michigan is the sand reed, Ammophila arundinacea, 
The life history of an Ammophila dune will now be given, and 
may be taken as the average life history of a stationary beach 
dune. Whenever a tuft of this or any similar grass gets a foot- 
hold on the upper beach, the sand drifts along and is lodged in 
between the stems and leaves, as already described (see fore- 
ground, fig. g). The leeward trail of sand changes its position 
as the wind varies its direction, but the sand deposited between 
and around the blades of grass is not easily dislodged. The 
radial propagation of the tuft of grass causes an areal extension 
of the miniature dune. So, too, there is an increase in altitude, 
since the grass constantly grows higher in its endeavor to lift 
itself above the sand. This upward growth enables more sand 
-to accumulate; in other words, the grass and the dune grow fan 
Passu outwards and upwards. The result of several years of this 
symbiotic growth of dune and grass may be seen in jig. 4 which 
represents a small embryonic dune on the beach at South Chi 
cago, Ill. The general contour of the dune is seen to be deter 
mined by the Ammophila; toward the left is the leeward tral 
of sand left by the last wind. fig. 3 represents an older and 
larger Ammophila dune on the same beach, viewed from the 
lakeward side and hence not showing any leeward trail of sand. 
Not only is the general contour of this dune determined by the 
Ammophila, but there will be observed a somewhat sinuous 
trough toward the center, where there happens to be 0 vegeta 
tion. This shows how readily the dune would be removed were 
it not for the plant life present. Thus Ammophila is not only 
an efficient dune-former but also a dune-holder. Bp 
While Ammophila is the most common dune-formet 
perhaps the best adapted for that difficult task of all ouf . 
shore plants, many other species play a similar réle. On" a 
northern beaches Agropyrum dasystachyum is very common aa 
dune-former; its habit is exactly that of Ammophila, and conse: 
quently needs no description. : Elymus Canadensis and Cala 
srostis longifolia may be regarded as dune-formers, but Lil 
are of less importance than Ammophila and Agropy 
