THE NORTH TEMPERATE ZONE 103 



scattered pines begin to appear and finally form an open forest. 

 This gradually is replaced by a mixed hard-wood forest as the 

 moister coastal region is approached, and cypress swamps become 

 frequent, in which one sees the fantastic cypresses bearded with 

 the " Spanish moss" (Tillandsia). 



These cypress swamps are among the most striking plant as- 

 sociations of the country. They occur as far north as Virginia, 

 near the coast, and extend up the Mississippi Valley into southern 

 Missouri and Illinois. 



The bald cypress (Taxodium distichwn), is a large tree, often 

 growing permanently in water, but also in rich moist ground which 

 is not submerged. Where the base of the trunk is submerged, 

 there are developed on the roots, the " knees," conical outgrowths 

 which appear above the water, and serve for aerating the roots. 

 The young trees are very symmetrical in form, like most conifers, 

 but the older trees develop a very irregular and fantastically 

 branched crown rising above the other trees of the association. 

 In the wetter portions of the cypress association the principal 

 species are the sour gum (Nyssa aquatica) and an ash (Fraxinus 

 platycarpa), but oaks, maples, hickories, and some others also 

 occur. 



In the Gulf region, dense growths of the dwarf palmetto (Sabal 

 Adansonii) are common, and the branches of the cypress are 

 heavily draped with the dismal blackish streamers of Tillandsia. 



About the margins of the swamp are some showy herbaceous 

 aquatics. Passing through this region in early April, the writer 

 noted two handsome species of Iris (I. hexagona, and /. cuprea), 

 a white spider-lily (Hymenocallis), showy species of Phlox, Sen- 

 ecio, Oenothera and Lobelia, and magnificent masses of the royal 

 fern (Osmunda regalis) as well as several other ferns. 



In the river valleys of eastern Texas there is a hard-wood forest, 

 which in places is dense and with trees of large size; but westward 

 with the lessening rainfall, the forest disappears and the prairie 

 becomes dominant. Eastern Texas marks the westward limit 

 of the southern deciduous forest as well as the pine forest of the 

 coastal plain. 



The transition from the heavily wooded eastern states, to the 

 prairie states along and beyond the Mississippi, is a gradual one. 

 In southeastern Michigan, northwest Indiana, and much of Illi- 



