MARYLAND WEATHER SERVICE 253 



abundant upon the abutments of the canal bridge, and upon the 

 nearby cliff to a slight extent, Dianthera americana is common in 

 the margins of the Potomac, and near the mouth of the tributary 

 stream, forming compact beds close to the water, or just below its 

 surface, and the following additional species were noted : 



Allium cernum 

 Ambrosia trifida 

 Cuscuta gronovii 

 Verbena hastafa 

 Asclepias quadrifolia 

 Woodsia obtusa 

 Viburnum dentatum 

 Pellaea airopurpurea 

 Partlienocissus quinque folia 

 Micrampelis lobala 

 Acer negundo 

 Tradescantia virgin ica 

 Linaria linaria 

 Aquilegia canadensis 

 Asplenium trichomanes 

 Physalis lieteropliylla. 



Considerable seepage from the canal makes the ground below it 

 almost swampy in places, but no rare or unusual species were noted, 

 as these areas are usually accessible for use as pastures, or if too 

 steep for the latter, then covered with the normal river bank vege- 

 tation in somewhat greater luxuriance than in the drier places. 

 Many weeds become established along the canal, about the feeding 

 places of the canal boat teams, but as the plants so established are 

 of the common species to be seen in the hayfields or along the road- 

 sides elsewhere, it is hardly necessary to list them. 



North Mountain. 



The slopes of North Mountain are flanked by a series of lesser 

 hills and intervening valleys, in which the moisture conditions are 

 favorable to a rich growth of forest, and of herbaceous undergrowth. 

 There are few spots of sandstone bog pockets, such as were found 



