19 



seed about twenty years ago. The species was collected at 

 Toledo in 1878 by J. A. Sanford. (See Mr. Werner's note 

 in proceedings for 1892.) In character this Cress is a bad 

 weed, and is spreading rapidl}'. 



THE POISONOUS PLANTS OF OHIO. 



BY AUG. D. SELBY. 



A brief discussion of poisonous plants with an Ohio list 

 of poisonous species. (For a somewhat similar paper 

 by the same authoi» see Journal, Columbus Horticultural 

 Society. VIII: 110, 1893.) 



CETRARIA ISEANDICA (L.) Ach., A SURVIVOR 

 FROM THE GLACIAL TIME OF OHIO. 



BY EDO CLAASSEN. 



.By careful observations and examinations it was proven 

 that on the warm days of the tertiary period, there fol- 

 lowed in the greater part of North America a time of ex- 

 treme coldness, during which an area reaching from the pole 

 to about 88° latitude was covered with ice. Animals and 

 plants used to live and grow in a warm climate were killed 

 and destroyed by the then dominating low temperature; 

 other animals and other plants, however, inhabitants of a 

 colder climate, arrived, taking the place of the disappeared 

 ones in such localities, as did suit them. At that time, un- 

 doubtedly, we did have there, as nowadays far north, an 

 subarctic and arctic flora, which retreated north as soon as 

 the temperature in the.se regions did increase. This retreat 

 of the ice was surely not effected suddenly, but in accord- 

 ance with the by and by increasing temperature slowly; the 

 plants growing there had sufficient time to accommo- 

 date themselves to the circumstances and the changing cli- 



