MARYLAND WEATHER SERVICE 297 



general appearance of the plant assemblage and the relative abun- 

 dance of the species involved. There are nevertheless a few small 

 plants foimd only in the shade of deep forests which seem to be dis- 

 appearing as the virgin forests are destroyed, notably the Small 

 Enchanter's Nightshade (Circaea alpina) and the Twin Flower 

 (Linnaea borealis). On the other hand the clearing and cultivation 

 of the country with all its attendant activities has broiight about the 

 introduction from Europe, South America, our Western States and 

 elsewhere of a very large number of plants, most of which have be- 

 come a permanent part of our flora. These introduced plants belong 

 chiefly, though not entirely, to the class which we designate as 

 weeds, and owe their introduction and persistence to a high faculty 

 of withstanding adverse conditions of soil moisture and to a high 

 degree of adaptability to varying external conditions. As these 

 introduced members of our flora have found their way here they have 

 taken up as habitats the fields and other cultivated grounds, road- 

 sides and waste places, so that the plant assemblages which they form 

 are separate from the assemblages of native plants, whether or not 

 these are modified by man. It is very necessary in the study of a 

 highly cultivated area like Maryland to keep in view the modifi- 

 cations in the plant-life due to man. The number of species actu- 

 ally exterminated are few if any; the number introduced is large 

 but we know just which ones they are and, — with a few exceptions, — 

 they are distributed throughout the state. So far as concerns the 

 flora of the state, then, cultivation has made no change save a con- 

 siderable addition of species. As concerns the vegetation of the 

 state, however, the changes have been profound. 



The attempt has been made in the foregoing chapters to give some 

 notion of the character of the original vegetation of the various parts 

 of the state, so far as that may be reconstructed from the plant cov- 

 ering of today. The observation and study of vegetation has cen- 

 tered about virgin and other old growths of forest, swamps, marshes, 

 bogs, dunes and beaches, because it is only in such habitats that one 

 may find native plants in their natural relation to external con- 

 ditions and to each other. Inasmuch as every plant which is grow- 

 ing and reproducing has necessarily found conditions which are more 

 or less congenial to it, no matter by what means it came to be grow- 



