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 fieshy 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 difhcult, 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. 

 Chtetochloa glauca (L.) Scrib. 

 Cenchrus tribuloides L. 

 Eragrostis major Host. 

 Eragrostis purshii Schrad. 

 Polygonum aviculare L. x 

 Polygonum littorale Link, x 

 Amaranthus hybridus L. 

 Amaranthvts blitoides Wats, x 

 MoUugo 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. 



