TYPES OF PLANT-COMMUNITIES. 893 



I 



belonging to the first group, to which belong in particular many Composites, 



Caryophyllaceae, Chenopodiacese, Papilionacese, and Cruciferue, are multifariously 



branched from the very base (e.g. Artemisia, Gypsophila, Salsola, Melilotiis, Crambe); 



j the species of the second group have upright stems which are unbranchcd up to 



: the region of the flowers and bear entire leaves (e.g. many species of Verbcu^cavi, 



• Epilobium, (Enothera, Euphorbia), and the species of the third group pos.ses8 



erect stems which have few branches, or none at all, but bear variou.sly lobed and 



j compound leaves (e.g. Glycyrrhiza, Eupatorium, Tanacetum, Sambuctis Ebulas). 



I As regards the fourth or frondose type (c/. p. 888), we have already indicated 



certain varieties. In describing the different communities of this kind special 



j emphasis must be laid also on the circumstance of the green laminae being entire, as 



I in Petasites, Tussilago, Nelumbium, Asarum, Scolopendrium, and Saxifraga peltata, 



I or divided and incised, as in most Ferns, several Aroids, and a few Helleborea 



' We must also take into account whether the fronds or foliage-leaves are deciduou.s 



j or evergreen, as in Hedera and Helleborus niger. 



Ribbon-plants occur in great variety in both flowing and stagnant waters, be 

 they fresh, brackish, or salt. The general aspect of any particular aggregate of these 

 ribbon-like forms varies according to the area and shape of the foliage or thallus of 

 the species concerned, and particularly according to whether the stems or the stem- 

 like parts of the thallus are lax or packed close together so as to form a dense, 

 pulpy matrix. The most conspicuous examples of social species are MyriopliylliLvi 

 with pectinate leaves, the Pond-weeds (Potamogeton) and Zannichellias with filiform 

 leaves, the Pond-weeds with broad, translucent leaves (see vol. i. p. 551, fig. 136), 

 the Grass-wracks (Zostera), Vallisneria (see vol. i. p. 667, fig. 155), and Cymodocca, 

 also a few of the Mosses (e.g. Fontinalis), various species of Fiicus, Laminaria (see 

 vol. i. p. 588, fig. 139), Sargassum, Macrocystis, and Cystosira amongst Brown 

 Seaweeds, species of the genera Ceramium, Callithamnium, Polysiphmiia, and 

 Lemanea amongst Floridese, the species of Bryopsis and Caiderpa amongst the 

 Siphonese, and the several species of Ghara and Nitella amongst Stoneworts. 



The points whereon the classification of Reeds is based have been already 

 indicated on p. 888. A number of distinct forms may be distinguished according 

 as particular species of Horse-tail, Sedge, Rush, Restiaceoe, Scirpus, Calamagrostis, 

 &c., prevail. The drawing of a Papyrus -swamp on p. 747 may be taken as 

 typical of this class of vegetation. In the North Temperate Zone, of those which 

 grow on dry ground the most prevalent species are those of the genus Calama- 

 grostis. A great many Reeds occur in the Tropics and in the Steppe regions of both 

 the Old and the New World, especially in the pampas, llanos, &c. 



The plants which constitute the dominant members of carpet include both 

 Phanerogams and Cryptogams. Of the former the most important are the inter- 

 weaving and tussock-forming Grasses, Sedges, and Rushes, the interlacing, grass- 

 leaved CaryophyllacesB (e.g. Alsine Rosani, Cherleria sedoides, Silene acauli'^), the 

 species of Houseleek (Sempervivum) which form rosettes, the Saxifrages of the 

 Aizoon group, the loosely-woven delicate Saxifrages which grow near springs, and 



