1016 MINNESOTA BOTANICAL STUDIES. 



content of the soil, must be referred eventually, as one studies 

 the phenomenon, to the rounding 1 , polishing action of ice in the 

 Glacial period. Perhaps no better illustration than the differ- 

 ence in plant population between fine talus slopes and gravel - 

 slopes could be given to illustrate the antiquity and multiplicity 

 of causes that determine the plant-physiognomy of any given 

 region. 



ROCK SHORES. 



While many rocky shores show true zonal distribution of 

 their plant population, this is not usually the case. When the 

 surface of the rock is irregular, the whole split by a network 

 of crevices, and covered here and there with little pieces of 

 talus, a lack of symmetry arises which finds response in azonal 

 distribution of the plants which tenant the area. 



Irregular surfaced rock shore. Very often the irregularity 

 of the surface arises from wave action, very often from weath- 

 ering, recent or preglacial, and in some cases it is the direct 

 result of glacial abrasion, as may be seen at the Northwest 

 Angle. However developed, the result is much the same so far 

 as concerns the distribution of plants. In the hollows and 

 crannies soil will collect, either by drainage- in or by adjacent 

 formation through the activity of lichens, mosses and ferns, 

 and these soil pockets, irregularly distributed, of varying 

 depth and extent, give rise to a considerable variety of plants. 

 A list of rock plants on the extreme northwestern point of Big 

 Island is given here to indicate what are the dominant species- 

 Rock group on Big Island point. 



Dryopteris thelypteris. Potentilla arguta. 



Polypodium vulgare. Kosa blanda. 



Juniperus sabina. Spiraea salicifolia. 



communis. Oxalis stricta. 



Taxus minor. Hypericum ellipticum. 



Agropyron tenerum. Chaniaenirion augustifolium. 



Agrostis alba Onagra biennis. 



hiemalis. Aralia racemosa. 



Elymus canadensis. Verbena bastata. 



Muhlenbergia mexicana. Mentba sativa. 



Panicnm dicbotomum. Stacbys aspera. 



Carex canescens. Vleckia anetbiodora. 



Cyperus strigosus. Plantago major. 



«J uncus tenuis. Galium bo real e. 



Unifolium canadense. Louicera dloica. 



Quercus macrocarpa. Campanula rotundifolia. 



Actaea alba. Ambrosia artemisiaefolia. 



Anemone canadensis. psilostacbya. 



Kanunculus macounii. Eupatorium perfoliatum. 



Capnoides micranthum. Euttaramia graminifolia. 



Arabis hirsuta. Hieracium canadense. 



Heucbera americana. Lactuca canadensis. 

 Cerasus virginiana. 



