90 Bulletin 1, Biological Society of Washington, 1918. 



tide pools, while such areas as the Pine Barrens of New 

 Jersey and Georgia are vast lagoons, and as it happens, the 

 chief reservoirs of a tide that is not yet wholly still, and 

 which may in future undergo movements similar to those 

 we must believe have occurred in the past. 



In conclusion, therefore, it seems clear that the Magnolia 

 Bogs of the vicinity of Washington harbor the survivors of 

 one or more of the plant waves ^^ that accompanied each 

 depression of the Atlantic Coast Region. The antiquity of 

 some of these little waifs and the vicissitudes they have 

 survived entitles them to our respect, while the slender 

 thread upon which their continued existence depends com- 

 mends them to our most considerate care. 



While the Magnolia bogs contain a large number of char- 

 acteristic Pine Barren plants, and the District of Columbia, 

 eastern Maryland, and Delaware together can boast repre- 

 sentatives of seven-tenths of the typical Pine Barren species, 

 there are no Pine Barrens in the region. The reason appears 

 to be absence of considerable areas of the necessary surface 

 deposits to permit extensive colonization of Pine Barren 

 plants and to protect them from competition with other types 

 of vegetation. 



OTHER TYPES OF COLLECTING GROUNDS IN THE 

 DISTRICT OF COLUMBIA REGION. 



The writer neither expects to replace, nor hopes to equal in 

 interest the delightful accounts of local collecting places that 



similar spots in the Coastal Plain which have been entirely and repeatedly 

 submerged. That they have been left in these places by a tidal movement 

 of the Pine Barren Flora, as above outlined, is the irresistable conclu- 

 sion. Probably the occurrence of numerous pairs of closely related species 

 in the Coastal Plain and Southern Appalachians may be taken as evidence 

 of a similar movement, and further as proof of a lapse of time since the 

 last commingling of the floras sufficient for the development of the diver- 

 gences now shown. It seems more natural to regard the Coastal 

 Plain rather than the region of Archean rocks as the ancestral home of a 

 flora which shows such pronounced dependence upon silicious soils. R. M. 

 Harper, especially, points out the probable recent origin of the Coastal 

 Plain flora (Ann. N. Y. Ac. Sci. 17, Pt. 1, 1906, pp. 11-13). 



8^ This tidal movement of plants occurred along our whole Atlantic 

 Coast, and evidences of it as far North as Labrador, together with an 

 interesting discussion of the matter have been published by Professor M. 

 L. Fernald. (Rhodora, 13, July, 1911, pp. 1J5-162.) 



