44 Proceedings of the Columbus Horticultural Society. 



The relation of the Flora of the Northeastern United States 

 to that of Europe is very marked ; Ohio as a member of this 

 region, which has gradually come to be called the " Manual 

 Range" (latterly extended west to the 100th meridian) par- 

 takes likewise of this similarity in its Flora. 



There are, (Gray I), of indigenous plants, 180 species of 

 dicotyls, 141 species of monocotyls and 20 species of ferns 

 common to the Northeastern United States and Europe or 

 341 species in all three classes of plants ; of these 150 species of 

 phanerogams and 16 soecies of ferns and allies are found in 

 Ohio. 



According to views held generally by naturalists these rela- 

 tionships between the Flora of Eastern North America, 

 including Ohio, and those of Europe and Asia as already 

 pointed out, indicate that in the past histories of the floras of 

 these regions, there has been a common source from which 

 the plants of the several countries have arisen. Allowing for 

 the relation between allied forms and like topographical, 

 geological and climatic conditions there yet remains the dis- 

 position everywhere shown by naturalists, to refer identity of 

 form to similarity of origin. By this is meant not only to 

 similar conditions under which alone these resemblances would 

 be maintained if once possessed, but to refer the plants to 

 identical progenitors. Or to state it in another way, it is held 

 that the effect of environment is to modify pre-existing forms, 

 not to create new ones outright. When, therefore, similarity 

 or identity of species is found, as in the case cited, like condi- 

 tions of growth alone will not explain their occurrence. Com- 

 munity of origin is likewise called for. 



For us in the present instance, this means that at one time 

 the progenitors of the plants of Japan. North China, and the 

 progenitors of the plants of Ohio, or a large number of them, 

 grew together in the North Polar region, whence they were 

 forced southward by the gradual change of climate which was 

 here during the glacial epoch. The studies of palaeontologists 

 have shown similar fossil plants in deposits within the Artie Cir- 

 cle, and there is abundant evidence of the former existence of a 

 flora like our present one in these high latitudes. Assuming that 

 such plants were driven to new conditions they would be modi- 

 fied by ecological adaptations. Furthermore, plants from the 

 north have met those typical of more southerly situations ; 

 the former have receded with returning warmth and have 

 carried the latter with them. Our fiora appears clearly to 

 have been the meeting point of plants from the northeast and 

 from the northwest. These have been met in turn by planst 

 from the east, often originally from the northeast, from the 



