30 Holm Additions to the Flora of Washington. 



These species belong almost exclusively to the fourth category, 

 under which Professor Ward (1. c., p. 14) has designated a num 

 ber of plants which he thought had either been exterminated or 

 had accidentally disappeared since the publication of the Pro- 

 dromus. Some of these plants are now known to be quite abun 

 dant in certain localities ; for instance, Apocynum androsaemi- 

 folium, Rhexia mariana, Polygala verticillata, Polygonum tenue and 

 Cyperus flavescens. 



This fact seems to show that the flora of the District is yet 

 but imperfectly known. There are, indeed, many and most in 

 teresting localities that have not yet been explored, and I will 

 merely recall the fact that the southern and southeastern part 

 of the District is still almost unknown. There is that interest 

 ing locality where Mr. G. W. Oliver obtained so many rare 

 plants, which was recorded in the third addition as " the vicinity 

 of Silver Hill." 



This locality comprises the large forests, with creeks and 

 sphagnum swamps, which lie between Silver Hill post-office and 

 Surattsville, Prince George's county, Md. A visit to these forests 

 shows us only too clearly that there is certainly a good deal of 

 work to be done before we should venture to declare that we 

 know our local flora. We meet here with species which are 

 either not recorded in Professor Ward's flora or only enumerated 

 as rare and of which several have been observed to occur in the 

 greatest abundance, such as Ilex glabra, Rhyncospora cephalantha, 

 Agrostis elata, Uniola gracilis, Aristida purpurascens, Xyris flexuosa, 

 etc. The same is the case with several other places which have 

 only been lately explored. Brookland, for instance, is the home 

 of twenty species of Panicum, several of which have never been 

 noticed before, although they are very common; there grow, 

 also, Apocynum androsaemifolium, Sporobolus vaginseflorus and 

 Agrostis elata quite abundantly. 



But, besides these truly indigenous species, I have also noted 

 some others, which have been accidentally introduced e. g., 

 Tribidus maximus * and Leptochloa mucronatarf both of which ap 

 peared suddenly in the Agricultural grounds. Leptochloa was 

 very abundant, with ripe seeds, and it may, therefore, also spread 

 to other parts of the city and become a well-established citizen. 



Among the species enumerated in the following list are several 



* Found by G. H. Hicks, 

 f Found by the author. 



