132 JOURNAL OF THE ARNOLD ARBORETUM (vol. n 



aided in their up-stream migration by southerly winds, it is doubtful 

 if any of the more southern forms can make much headway here, with 

 the clijnatic handicap, in competition with more hardy species. The 

 inference then seems reasonable that the typically southern species found 

 in Southern Illinois and adjacent areas in Missouri, Kentucky and Indi- 

 ana, have not invaded the region by a northward extension of their range 

 in comparatively recent times, but on the contrary are survivors of a 

 more numerous association that flourished liore in the remote past, when 

 climatic conditions were much more temperate and favorable to them. 

 It seems safe also to assume that few, if any, of the extra-Hmilal species 

 are increasing in numbers or are extending their range within the salient 

 at present, but in fact are gradually loosing ground through tlic destruc- 

 tion of their most exposed outi)osts in seasons of long continued drought 

 or extreme cold — losses which they are unable to make good against the 

 constant pressure of more hardy species. This process is also being 

 greatly facilitated by the inroads of civilization: in the draining of swamps, 

 clearing of forests, and probably also through the introduction of new 

 insect and fungus enemies that help to turn the tide against the archaic 

 species in the unecpial combat they are waging in a somewhat too rigor- 

 ous climate. 



In the extreme southern part of Illinois, where the Ohio River joins 

 the Mississippi, and in the big bend of the latter to the west, are extensive 

 tracts of alluvial bottom lands, interspersed with swamps and lakes, 

 the latter evidently renmants of former river channels. Similar areas 

 persist, with a slight interruption in the vicinity of Thebes, along the 

 Mississippi River as far north as Grand Tower, and for some distance 

 uj) the valleys of Cache River and Big Bay Creek, small tributaries of 

 the Ohio. Lowlands and swamps of consideralile extent arc also found 

 along the Ohio, north of tlie Shawnee Hills, from the Saline River to 

 above the mouth of the Wabash. Most of this area is, or was before the 

 days of lc\ ecing and drainage, subject to frequent inundations, and along 

 the lower levels and old channels water accumulated, forming permanent 

 sloughs and swamps. 



A magnificent forest of deciduous species originally covered these areas 

 of swamp and lowland: in density of growth and size of individuals it 

 was scarcely surpassed by anything north of tlie tropics; and it is here 

 that nearly all of the typically southern si)ecies are found. 



One of the most remarkable and quite the most conspicuous of the 

 southern trees of this region is the Cypress {Taxodium disfichvm). It 

 was formerly very abundant in the deep swami)s and in shallow water 

 along the margins of lakes, sloughs and small streams in all of the south- 

 ern counties; and on the eastern side it extended northward along the flood 

 plain of the Ohio River as far as the mouth of the Wabash. Some of the 

 trees here grew to an enormous size, and with all the characteristics that 

 mark the species in its most favored haunts in the extensive swamps of 

 Mississii)pi, Louisiana and eastern Texas. Specimens from one hundred 



