210 THE PLANT LIFE OF MARYLAND 



the favorite habitat of the Hemlock and the Butternut, as well as 

 a number of herbaceous plants which were doubtless much more 

 common in the virgin forests than they are now, but are still 

 abundant in the Upper Midland District. Among these may be 

 mentioned : Saxifraga pennsylvanica, Panax trifolium, Hieracium 

 paniculatum, Capnoides scmpervirens, Parietaria pennsylvanica, 

 Trautvetteria carolinensis, Asplenium trichomanes, Sedum terna- 

 tinn. 



FLOOD PLAINS. 



The Flood Plain areas of the Lower Midland District are dis- 

 tributed along all of the constant streams, varying in breadth 

 with the size of the stream from a few feet to as much as half a 

 mile at some localities along the Potomac. Their rich alluvial 

 soils maintain a high percentage of moisture and have the ground 

 water level within a few feet of the surface, but the surface layers 

 of the soil are seldom continuously saturated, as is the case with 

 many of the Flood Plains of the Wicomico terrace on the Eastern 

 Shore. The inundation of the Flood Plains is frequent during 

 the spring and summer, but is always of very short duration on 

 all but the largest rivers. 



The Flood Plains were all originally heavily wooded with a for- 

 est rich in tree species. The Tulip Tree, Red Maple, Swamp Oak, 

 Black (ruin and Slippery Elm, and White Elm are the most 

 common forms and together make up 80% of the stand in most 

 of the Flood Plains examined. Other characteristic species are 

 i he River Birch, the Hornbeam, the White Ash, the Bitternut Hick- 

 ory and the Green Ash. The Box Elder is abundant in the Flood 

 Plains about the head of the Elk River and along the Potomac, 

 but has not been noted in the other parts of the Lower Midland 

 District, although it occurs in the Western Shore District of the 

 Coastal Zone. Other infrequent species are the Willow Oak, which 

 only occurs along the Potomac as far as Seneca Creek; the Shingle 

 Oak, which is not infrequent in Montgomery County in the vicin- 

 ity of Gaithersburg and the Great Falls, but is known elsewhere 

 in the state only from Zekiah Swamp, in Charles County; and 

 the Swamp White Oak, which also occurs in the Upper Midland 



