266 
The Ohio Naturalist. 
[Vol. V, No. 3, 
without a central stem but with a number of prostrate radiating 
branches. Sometimes there is a central erect stem a few inches 
high with long prostrate branches radiating in all directions from 
the base. The same form has been seen by the writer on sand- 
hills in central Kansas. So peculiar is the appearance that one 
hardly recognizes the plant in its new form. Eragrostis purshii 
Schrad. and Diplachne acuminata Nash also form mat-like bodies 
when growing on sandbars. On exposed broken ground various 
normally erect, ascending, or decumbent plants also form mats. 
Noteworthy among these are Echinochloa crus-galli (L.) Scrib., 
Eragrostis major Host., and Cenchrus tribuloides L. In salt 
marshes of the interior one meets with fleshy mat plants like 
Sesuvium sessile Pers. Sesuvium martimum (Walt.) B. S. P is 
common on the sands of the Atlantic coast. Dondia depressa 
(Pursh) Britt, is also a fleshy halophyte which commonly assumes 
the mat form on the salt marshes of Kansas. 
It should not be difficult, with suitable physiological exper- 
iments, to determine the ecological factors which induce the for- 
mation of mats. Intense light and unobstructed space appear to 
be very important. The wind may have some influence. Water 
supply appears to have little or no effect. Thus Eclipta alba (L.) 
Hassk. was observed to form perfect mats on very wet exposed 
sandbars but in shaded situations a little distance away it grew 
entirely erect, some plants being three feet high. 
The Ohio plants named below are either typical mats or 
develop as mats under proper conditions. The more typical spe- 
cies are marked with an x. 
Echinochloa crus-galli (L.) Beauv. 
Ch;etochloa glauca (L.) Scrib. 
Cenchrus tribuloides L. 
Eragrostis major Host. 
Eragrostis purshii Schrad. 
Polygonum aviculare L. x 
Polygonum littorale Link, x 
Amaranthus hybridus L. 
Amaranthus blitoides Wats, x 
Mollugo verticillata L. x 
Portulaca oleracea L. x 
Alsine media L. x 
Euphorbia polygonifolia L. x 
Euphorbia serpens H. B. K. x 
Euphorbia maculata L. x 
Euphorbia humistrata Engelm. x 
Euphorbia nutans Lag. 
Verbena bracteosa Mx. 
Spermacoce glabra Mx. 
Diodia teres Walt. 
Eclipta alba (L.) Hassk. 
