294 MINNESOTA BOTANICAL STUDIES 



Galium trifidum, G. triftorum, Tencrium occidentale, Stachys pains- 

 iris, and Scutellaria galericulata. 



The more alkaline situations freciuently show a broad belt or 

 scattered patches of Scirpus americanns inserted between the marsh 

 formation and this association. This plant is often as exclusive as 

 Eleocharis palustris. Very commonly also this species becomes 

 dominant in depressions well within this association. 



Clearly defined societies of the halophilous Triglochin maritima 

 and Plantago eriopoda are common over low, flat divides between 

 alkaline lakes and ponds in many of the wet valleys. The former 

 species often reaches such a degree of abundance as to produce an 

 extremely tenacious sod in a soil that is so alkaline as to show 

 crystallized material on the surface. The common salt grass, Dis- 

 tichlis spicata, is also commonly found in similar situations covering 

 wide expanses with its close sod to the exclusion of all other species 

 of plants. A peculiar tall, slender, and difTiise form of the salt 

 grass was found in stands of Scirpus americanus and other taller 

 members of this association. This form is so noticeably different 

 from the usual habit of the species as to appear as an entirely differ- 

 ent species upon first sight. 



A contrast effect produced by a species of this association must 

 be mentioned in closing. Agrostis hyemalis is a frequent and abun- 

 dant member of this association which often exhibits a very per- 

 fectly belted type of distribution. These belts are conspicuous about 

 many of the lakes. The regular position of the belt is immediately 

 back of the marsh formation where there is a rather short transition 

 to a little higher, harder land on the shore. The inner portion of 

 the belt is usually very clean cut, but toward the uplands the individ- 

 uals gradually dwindle away until the belt is lost in some other 

 aspect of the association. These belts, which are sometimes 30 feet 

 or more broad, are especially conspicuous because of the stretches 

 of densely tangled, light-purplish to bright straw-colored panicles 

 which contrast vividly against the dark green background. 



THE WATER HEMLOCK ASSOCIATION 



■This is essentially the "water hemlock formation" of Pound 

 and Clements. In the regions of ponds, lakes, marshes, and wet 

 meadows, and locally also along some of the stream courses, Cicuta 

 occidentalis is sometimes developed to a decidedly controlling 

 degree. The plants of this species tower above the many lower wet 



