1922] WATERMAN—PLANT COMMUNITIES 25 
GRASS MEADOW TYPE.—Here the fourth stage is one dominated 
by grasses and sedges forming a relatively solid turf. In the small- 
est depressions the sedge society may be only a few yards square, 
and in it there are often found swamp plants such as Hypericum 
virginicum, Spiraea salicifolia, and Rosa carolina, as well as occa- 
sional relics of the aquatic stages. The later stages resemble those 
of the swamp type already described. The larger grass meadows 
are relatively limited in number, only four or five having been dis- 
covered so far, and they have certain peculiar features which seem 
to demand special consideration. The first is the mature condition 
of the extensive grass turf, and the other is the absence of any 
tendency of the shrubs and trees to invade the meadow. Where 
the grass meadow is surrounded by a shrub zone of the swamp type, 
this may be accounted for on the assumption that the depression 
was originally all very shallow, thus favoring a development of turf 
so rapid that the shrubs and trees had no chance to become estab- 
lished before the mat of grass roots had completely occupied the 
substratum. There are, however, some features which indicate 
that the grass mat was formed recently and very rapidly, indicating 
perhaps a physiographic change in comparatively recent times. 
These are best shown in a grass meadow visited only once, as it was 
discovered in a hurried reconnoissance trip, and so far there has 
been no opportunity for a second visit. This meadow is located 
just west of the lower reaches of the Platte River very near the 
strip of moving dunes on the shore. It extends from northeast to 
southwest practically in a straight line for rather more than half a 
mile, but is less than a hundred yards wide at the point crossed, 
although somewhat wider to the east and the west. At this point 
there were imbedded in the grass on both edges of the meadow 
trunks of dead trees extending out from both banks, and on each 
tree was growing a row of tamaracks apparently not over twenty- 
five years old. There were scattered tamarack trees on the lower 
edges of the sand ridges. While the localization of the tamaracks 
on the dead logs and not in the grass is not surprising, the preserva- 
tion of the logs long enough for the grass turf to form and the 
apparent youth of the trees makes a very interesting problem. 
This meadow apparently has never been mowed or burned. The 
