igo HELOPHYTES sect, v 



in which he distinguishes associations of Typha-Sagittaria along the 

 rivers, and of Scirpus-Erianthus at the edge of the swamp-forest. Here 

 also occurs Arundinaria macrosperma - association, which clothes large 

 expanses of the Dismal Swamps. Along the rivers of Pennsylvania, 

 according to Harshberger,^ there occur extensive reed-swamps, in which 

 he distinguishes various associations, including those of Zizania, of 

 Typha, of Sagittaria latifoHa, and of Ambrosia trifida. In swamps with 

 slowly flowing water one finds other associations, including those of 

 Symplocarpus (with Spathyema foetida, and species of Osmunda), of 

 Iris-Typha-Acorus, and of Heracleum-Veratrum-Eupatorium. Every- 

 where the physiognomy, and to some extent the genera, are the same as 

 in Europe. 



ASSOCIATIONS IN TROPICAL ZONES 



Other species and families occupying similar habitats play the same 

 part in nature within the tropics, but, as their associations include entirely 

 different forms, they present a different physiognomy. They have been 

 studied only to a slight extent. Many species of Araceae are swamp- 

 plants just as are Calla and Acorus in Europe and usually have sagittate 

 or cordate leaves ; dense associations, often several metres in height, are 

 formed by them, for instance by Montrichardia arborescens in Trinidad 

 and the adjacent parts of South America, also by Caladium.^ Among 

 Scitamineae, species of Heliconia likewise occur in tropical America, and 

 gigantic Amaryllidaceae, represented by Crinum, fringe the rivers of 

 Guiana. These types of vegetation are never absolutely pure ; other, 

 possibly many other, species mingle with those that have been mentioned 

 as giving the tone to the vegetation. In the tropics larger numbers of 

 woody plants occur and affect the appearance of reed-swamps. But 

 there are also swamps with grasses and perennial herbs very like those 

 of temperate countries, for example in Brazil.^ 



CHAPTER XLV. BUSH-SWAMP AND FOREST-SWAMP OF 



FRESH WATER 



In reed-swamp and low-moor there often occur some woody plants, 

 but in other places these become so numerous as to create hush- 

 land and forest (woodland-swamp, paludal forest, foHage-moor). In 

 North Europe the first steps towards these are shown in collections of 

 alders, birches, and willows growing on the banks bounding fresh water. 



Alneta may occur on mud on which only few plants can thrive as 

 undergrowth ; these latter include ferns, mosses, Calla, Lythrum, 

 Spiraea Ulmaria, Menyanthes, Carex, and others, which particularly 

 grow on the drier spots at the foot of the alders. Intermingled with 

 the alders there may be species of SaUx, Viburnum Opulus, and Rhamnus 

 Frangula. In other spots Urtica dioica forms impenetrable thickets.^ 



Saliceta at other places in North Europe form the riparian bush- 



Harshberger, 1904. ' Martius, 1840-7. ' Warming, 1892. 



* See Domin, 1904. 



