SCIENCE-GOSSIP. 



79 



PLANTS AND ANIMALS OF DIFFERENT SOILS. 

 By H. Franklin Parsons, M.D., F.G.S. 



(Continued from page 42.) 



""THE silicious rocks, such as sandstone, sand 

 and grave], tend to form by disintegration a 

 light, dry, powdery soil. The character of the 

 soil, however, varies according to the size of the 

 particles of the bed and the readiness with which 

 it undergoes disintegration. Thus, a gritstone, or 

 a sharp gravel or sand, yields a thin, poor soil ; 

 while a loamy sand, such as the Thanet sand, forms 

 a warm and kindly one. A light, dry, sandy soil 

 is favourable to the germination of minute seeds : 

 hence sandy cornfields are frequently full of annual 

 weeds, such as the poppy. Sandy commons are 

 the especial habitat of dwarf annual plants, like 

 the various species of Trifolium and of Cruciferae 

 and Caryophyllaceae. A wet sand, on the other 

 hand, such as is met with where a layer of retentive 

 clay beneath holds up the water, tends to form a 

 peaty soil, and many of the same plants grow on it 

 as grow on peat. There are others, however, 

 chiefly of a dwarf growth, which prefer a wet 

 sandy soil to pure peat ; examples being Montia 

 fontana, Peplis portula, Anagallis tenella, Salix repens, 

 Juncus bufonius and /. squarrosus. The contrast 

 between the flora of sandy and of chalky soils is | 

 as a general rule, strongly marked, though there 

 are some plants, such as the mulleins, of which we 

 have three species near Croydon, that love a dry 

 soil, but are not particular whether calcareous or not. 



The older and more consolidated sand-hills on 

 the coast are often the habitat of plants of a 

 calcareous type, which presumably find the lime 

 which they require in the fragments of sea-shells 

 mixed with the sand. The plants which make 

 their habitat on the loose sand-dunes are remark- 

 able for possessing long, tough roots, or widely- 

 spreading rhizomes, which fulfil a useful purpose 

 by binding the shifting sands together ; the sand 

 sedge (Carex arenaria) and marram or star grass 

 (Psamma arenaria) being noteworthy examples. 

 Of plants characteristic of a sandy soil, the foxglove 

 broom, corn marigold, wood sage and small sorrel 

 are familiar examples. The Scotch fir, though 

 probably not a native in the south of England, 

 flourishes and propagates itself freely in such a 

 soil, covering large tracts of the Bagshot sands in 

 western Surrey. The larger ferns, mosses and 

 fungi abound in damp woods on a sandy soil. A 

 loose sandy soil is favourable to the operations of 

 burrowing animals, such as rabbits and moles. 



Peat is a deposit of vegetable origin, formed in 

 cold, moist situations, usually on waterlogged sand 

 or silicious rock, less frequently or less perfectly 



on clay, and very rarely on limestone. It consists 

 almost entirely of the decayed semicarbonized 

 remains of plants, such as the small shrubby 

 Ericaceae, rushes and sedges, and the larger mosses, 

 especially Sphagnum and Polytrichum. "When free 

 from admixture with sand, it contains only a very 

 small proportion of mineral matter, as shown by 

 the trifling amount of ash left when it is burnt in a 

 heath fire. It may attain in bogs a depth of 

 twenty feet or more, though it shrinks greatly 

 in thickness on drying, when the bog is drained. 

 It is, however, not very readily permeable by 

 water. A peaty soil is generally covered by brown 

 heathery moorlands. The vegetation is marked 

 by a comparatively small number of species present, 

 though each species is represented by a profusion 

 of individual plants ; also by the rarity of grasses 

 and plants with yellow flowers, and by the almost 

 total absence of pasture plants and of the weeds 

 of cultivation. The birch is the prevalent tree. 

 Among characteristic plants of the peat may be 

 mentioned the sundews, cross- leaved heath, bog 

 asphodel, bog violet, bog myrtle, and the grasses 

 Molinia caerulea and Nardus stricta. 



A clay soil is typically heavy and impervious to 

 moisture. A pure, stiff clay forms naturally a 

 poor, cold, backward soil ; but by cultivation, 

 admixture with lighter materials and manuring, 

 such a soil can be greatly improved. Clay is very 

 retentive of organic matter, whereas in a light soil 

 such matter is soon oxydised and disappears. 

 Hence the effects of manuring last longer in a clay 

 soil than in a sandy soil. A clay basis containing 

 a greater or less proportion of fine sandy matter is 

 called a loam, and one containing a proportion of 

 calcareous matter, a marl. The flora of a pure 

 clay is comparatively poor in species, and is 

 marked less by the presence of particular plants 

 characteristic of clay than by the absence of those 

 characteristic of limestone and sand. Most of the 

 plants which one finds on a clay soil are, in fact, 

 common ones. The vegetation consists mainly of 

 bushes and trees, or of strong-growing perennial 

 plants, often with creeping underground rhizomes 

 like the coltsfoot, couch grass and horsetails. The 

 floras found on loam and marl approach respec- 

 tively those found on sand and limestone. There 

 are, however, a number of plants which prefer a 

 heavy soil, though not confined to a pure clay. A 

 familiar instance is the primrose, which is absent 

 from the sandy and gravelly tracts of West Surrey, 

 but is plentiful, where it has not been exterminated, 



