PAPERS ON BOTANY 135 



almost be counted on one hand. It does not appear reasonable 

 to explain by any survival theory when the one here stated is so 

 tenable. (B.) 



A few of the species named are plainly the outposts of dis- 

 tribution, although it is very probable that in preglacial days, 

 this distribution might have been far more extensive. The 

 Canoe Birch arid Mistassinican Primrose are good examples 

 growing as they do on rocks untouched by the great ice cap, and 

 ending abruptly in Jo Daviess with the advent of the drift. 

 Such species are 1, 11, 24, 23, 24, 26, 28, 44, 46. (C). 



The deep rock cuts of the Illinois Central railway furnish 

 an artificial habitat closely simulating the natural cliffs, and 

 it is easy to understand how Pellaea and Woodsia would 

 flourish in such surroundings when once established. The 

 question, however, is not so easy of solution, for how did the 

 spores reach the cut east of Freeport nearly forty miles from 

 natural growth? (D. C or A?). 



Doubtless a few examples representing all that are left of 

 an original host of plants that through the advance of culti- 

 vation and consequent destructions of suitable places of 

 growth, have finally diminished to their present inconsiderable 

 proportions. Such are 10, 14, 15. (E.) 



A few are plainly a relic of the ice age, having been pushed 

 southward by the ice and on its retreat scattered remnants 

 persisted here and there. This is particularly the case about 

 the head of Lake Michigan, and may account for such plants 

 as numbers 13, 16, 18. (F.) 



The majority of the balance may be considered remnants or 

 survivals of a very much more extended flora that from many 

 varied causes have been exterminated, and these last repre- 

 sentatives, leading an uncertain existence until they too disap- 

 pear, and the species vanish from such localities forever. The 

 very peculiar isolated cases of the rattlesnake plantain, the 

 pipsissewa and the coral root in the Jo Daviess flora may be 

 such. Here it is highly probable the erosive agencies of flood 

 and ice have carried to destruction the intervening stations, 

 so that the isolation becomes much more pronounced. It may 

 be the Crjstatella comes here, but candidly no theory seems to 

 fit it exactly. Far from transportation lines, in a station so 



