66 



THE FERN BULLETIN 



while the greater part of the west is dependent upon 

 the Allegheny and Monongahela rivers, the union of 

 which at Pittsburgh, forms the great Ohio. 



The climate is somewhat subject to extremes, though 

 modified by differences in elevation. Heavy snow- 

 storms occur in the mountains in winter and as a re- 

 sult, the rivers, especially in the western section are 

 flooded in spring and early summer. This will recall 

 one of the most disastrous floods in the history of our 

 nation, that of Johnstown, in the southwestern portion 

 of the State, by which 2,209 lives were destroyed on 

 May 31, 1889. 



The distribution of the fernworts is influenced gen- 

 erally by local conditions, by the absence or presence 

 of the out-croppings of the various rock formations 

 and perhaps to a certain extent by climate, especially 

 with the species which find their southern limit of 

 range in Pennsylvania. Nearly one-fourth of the State 

 is wooded, the forests being fairly well distributed, 

 though the greatest lumbering regions are in the 

 northern part. It is to be expected, therefore, that 

 many w T oodland species occur throughout. The State 

 has been fairly well-worked, botanically, yet much re- 

 mains to be recorded, at least as far as plant distribu- 

 tion is concerned. From the standpoint of the fern 

 student, the flora is an extremely interesting one. The 

 geographical position of the State is such that quite a 

 number of northern species find their southern limit 

 within its borders, while some southern forms just 

 pass north of its limits, giving it a goodly admixture. 

 Among others Pellaea gracilis and Polystichum 

 Braunii manage to creep over the northern border on 

 the tops of the Alleghenies, though it is stated in "The 

 Fern Flora of New York" (Fern Bulletin, October, 



