THE HABITAT. XI. 



variation which are produced by climate, mainly because the climate 

 itself does not vary in a sufficiently marked manner, even in such a 

 diversified area as one finds in Dumfriesshire. My original scheme has 

 been therefore modified more than once, and in its final form consists 

 in pointing out the following factors for every species soil, exposure to 

 wind, and exposure to sun. Insect visitors, really an essential part of 

 the environment, are treated of by themselves. 



These three leading factors of the habitat are found inextricably 

 mixed in practice. The most usual combinations in Dumfriesshire are 

 the following : 



1. The Seashore (sand, shingle, estuarine mud flats, and rarely cliffs 



of boulder clay ; or, in Galloway, of rock). 



2. Holms (flat river-alluvium) roadsides and arable fields on boul- 



der clay. 



3. Ordinary Arable Land extending from sea level to about 800, or 



rarely 900 feet. 



4. Permanent Pasture or sheep farms, chiefly on silurian rock or 



drift, and extending from about 800 feet to the lower level of 

 the peat-haggs. 



5. Woods and Linns, from about sea level to nearly 800 feet. 



6. Carries and Glens, or mountain ravines, from 800 to 2200 feet. 



7. Peat Mosses and Ifaggs, at almost all elevations from nearly the 



sea level at Lochar Moss, and forming a thick capping over 

 all the highest hills of the district. 



8. Crates and Scaurs of bare whinstone rock or mudstones ; occa- 



sionally screes and accumulations of broken boulders and 

 stones. 



9. Railway Stations and Tracks, as well as waste ground generally. 



10. Lochs and Rivers. 



A large proportion of the Flora is rigorously confined to one or 

 other of these divisions. Unfortunately the meteorological and geolo- 

 gical factors are so insufficiently known that one cannot in any manner 

 obtain data of the degree of moisture of the soil or atmosphere, the wind 

 exposure, the amount of sunlight received, the porosity and fertility of 

 the soil, or even its geological character in any one of them. Without 

 distinct data on these points it is useless to attempt to draw up statistics 

 of the general characters of leaf, branching, or inflorescence found in 

 these particular habitats which would be, if possible, of enormous 

 importance. 



As regards plants, the different effect of light, heat, and wind ex- 

 posure can scarcely be distinguished in the field, because, e.g., shelter 

 from wind brings in its consequence rank vegetation, whether as a wood 

 or as in a corn field, and rank vegetation means a certain amount of 

 shade and a moist atmosphere. Shade in the same way involves wind- 

 shelter and a lower temperature. It is for this reason that exposure is 

 the most convenient term available. 



