CHAP. XLV FRESH-WATER BUSH- AND FOREST-SWAMP 191 



lands, mainly composed of species of Salix, S. alba, S. fragilis, S. cinerea, 

 and S. pentandra, between which there grow dicotylous perennial herbs, 

 including Lysimachia vulgaris, Epilobium hirsutum, species of Valeriana, 

 and Spiraea Ulmaria, as well as grasses such as Calamagrostis lanceolata 

 cind Phragmites. The lianes in these bush-swamps are Solanum Dul- 

 camara, Convolvulus sepium, and Humulus Lupulus. 



Betuleta and Pineta, according to Fleroff,^ occur on bog-lands in 

 Russia. 



More extensive bush-swamp and forest-swamp occur in the southern 

 part of the United States, where they give rise to large forests on wet, 

 peaty soil. In Virginia there are two main associations juniper-swamp 

 and black-gum swamp with several (subordinate) associations.'^ 



Juniper-swamp is formed of Chamaecyparis thyoides, and may be 

 pure. The soil is a very acid peat, which even in summer is covered by 

 water 30-60 centimetres deep. 



Black-gum swamp is composed of Nyssa biflora and Taxodium 

 distichum. On the horizontal roots of the latter there arise conical 

 roots which attain a height of a metre, are similar to those of Bruguiera 

 in mangrove-swamps, and in like manner serve as respiratory organs. 

 On the mud they form the solitary firm spots over which man can walk. 

 Many pseud-epiphytes occur on the trees.^ In the water between the 

 trees grow Azolla, Wolfhella, and others. The soil is acid, but not so 

 peaty and dry as in juniper-swamp. The water as a rule forms a sheet 

 jo-ioo centimetres deep lying above the soil. Nyssa and Taxodium 

 are deciduous. And the same is mainly true of the subordinate species 

 in Virginia. Farther south there appear a number of evergreen shrubs, 

 and several short palms, including Sabal and Chamaerops; near the tropics 

 Tillandsia usneoides and other epiphytes show themselves on the tree- 

 crowns. Nearly all woody plants growing in the American forest- 

 swamp are protected against rapid transpiration. Stomata in nearly all 

 species occur exclusively on the lower face of the leaf, and are sunken 

 m some species. In addition, the following features are present : coating 

 of hairs or of wax, thick cuticle, and thick outer wall to epidermis, con- 

 version of epidermal cells into mucilage, hypoderma, multiplication of 

 the pahsade-layers. This strong development of measures guarding 

 against desiccation is a consequence of acidity of soil, which abounds 

 in organic remains. 



Bamboo-forest (bambusetum). Tropical bamboo-forest must 

 apparently be regarded as one type of association belonging to swamp- 

 forest. Tropical rivers are often fringed with bamboo-brake, which 

 forms most impenetrable vegetation. Humboldt mentions that, along 

 the river Magdalena, there are uninterrupted forests of bamboo and 

 banana-leaved species of Heliconia. 



Nipetum. Under this heading is included the eastern Asiatic and 

 .\ustralian vegetation composed of Nipa fruticans. This palm is all 

 but stemless, yet it possesses immense pinnate leaves, which may be 

 six metres in length, and its growth may be so dense that one requires 

 an axe to cleave a way through the vegetation, in which other species, 

 mcluding Chrysodium aureum, also occur. Nipetum lies on the land- 



' Fleroff, 1907. * Kearney, 1901. ^ Thco. Holm, in letter. 



