NOTES OX EECENT EESEARCH. 



500 



(Smilax liispida), Grapes (Vitis sp.), Virginia Creeper {Ampelopsis 

 quinquefoUa) and Poison Ivy (Bhus Toxicodendron). 



Among the shrubs of the undergrowth, which is abundant from the 

 moist soil, are various species of Cratcegus, Bibes Cynoshati, &c. The 

 herbaceous vegetation is mainly vernal, as the shade is deep. Prominent 

 among it are Trillium recurvatum, Phlox divaricata, Polemonium reptanSy 

 Mertensia virginica, Claytonia virginica, Erythronium album, Ariscema 

 triphyllum and A. Dracontium, Nepeta Gleclioma, Viola cuciillata, Galium 

 Aperine, Urtica gracilis, kc. ; various umbellifers of the genera Heracleum, 

 Sanicula, &c., and the Dodder {Cuscuta Gronovii). 



Flood-plains sometimes consist of meadows instead of forests. Besides 

 various grasses, such as Poa pratc7isis and Agrostis alba, vulgaris, 

 Thalictrum purpurascens, Fragaria virginiana, and Anemone pennsyl- 

 ranica occur abundantly. Extensive thorn thickets (Cratcegus sp.) some- 

 times occur, probably betokening the beginning of a mesophytic forest. 



Though the last feature is the climax, retrogressions may take place 

 in connection with terrace formation. While deposition is the main 

 feature of flood-plains, erosion still continues, which causes vertical banks 

 in the flood-plain. It may thus swdng quite across its flood-plain, 

 destroying all that it has built, including the mesophytic forest, not only 

 by undermining and so felling the trees, but by draining the plain it 

 becomes more xerophytic. 



In making serpentine curves, " oxbow " lakes are formed by the river 

 breaking across the peninsula. Kiver-life is then soon replaced by pond- 

 life. 



The author next considers the Pond-swamp-prairie series. These are 

 all gradations between rapid streams and completely undrained ponds, 

 and corresponding with these various gradations are characteristic plant 

 species. 



No two floras can be more unlike in species or in adaptations than are 

 the typical brookside and swamp floras. Both hydrophilous, yet peat-bogs 

 have many xerophytic adaptations, such as leathery or hairy leaves, and 

 special structures for water-absorption. Schimper believes that these 

 structures are due to the difficult absorption in peaty soil, the humus 

 acids and the lack of oxygen being detrimental to normal root activities, 

 and the activities of soil-bacteria are lessened. Hence, peat accumulates 

 in consequence of the lack of drainage. 



The principal cause of the destruction of undrained lakes is vegetation. 

 According to the depth of the depression is an undrained swamp or pond. 

 In this latter Charas abound, as Avell as Water-lilies and Utricularias. 

 The rapidity with which the filling-up process of these plants is carried 

 on is striking, for the accumulation of Chara-peat amounts to 1 or 

 2 inches per annum. 



As the pond or lake becomes shallower, it becomes less fit for pond- 

 life, and the marginal flora invades it, such as Scirj^us lacustris, 

 Jilenyanthes trifoliata, and Potent ilia palustris. 



The next vegetation which follows consists of typical peat-bog plants, 

 as the leathery-leaved Cassandra calyculata. Then a tree zone of Larix 

 americana and Thuya occidentalis, then Pinus Strobus, S:c., advances upon 

 the last-named. 



