XU. THE HABITAT. 



The effect of exposure is most marked in the divisions one and 

 eight. Some characteristic desert adaptations, such as the rosette type 

 of plant, dense twiggy, cushion-like shrublets (which are really, I think, 

 to be considered as a bunch of rosettes supported on small branches), 

 fleshy leaves, and a coat of woolly hairs, are found both on the seashore 

 and on exposed rock ledges, as e.g., Raven craigs in Black's Hope. 



Spines and thorns, on the other hand, as well as the nameless type 

 represented by the seaside Euphorbias and Chenopodiaceae, do not, to 

 my knowledge, occur on the high exposed mountain ledges. 



This is probably because the last two are special adaptations against 

 or effects of strong sunlight, which may injure the tissues or chlorophyll, 

 while the others are protections against transpiration generally, whether 

 due to the wind or sun. 



The actual humidity of the atmosphere in the immediate neighbour- 

 hood of the sea must, unless I am greatly mistaken, be at some period 

 of the 24 hours far below that of the low-lying country and hills, and it 

 is not till the exposed rock summits of about 1500 to 2200 feet are 

 reached that there is the same amount of transpiration. 



The same condition of exposure, though it is not quite so clearly 

 marked, is obvious on (division nine) railway lines and all waste ground 

 which is kept clear of plants. It is obvious that in such places the con- 

 ditions of temperature and radiation of heat are extreme, and possibly 

 this explains the presence of such plants as Linaria minor, Tragopogon, 

 and Hieracium aurantiacum, which become yearly more abundant 

 along the different systems. 



The opposite extreme, that is of shade and shelter, is most marked 

 in number five, but in parts of number six there is considerably more 

 moisture even than in the lower woods, and I am rather doubtful 

 whether the separation is entirely justifiable. 



Probably the typical peat plants are more thoroughly represented in 

 Dumfriesshire than in any other county. Whether their characteristics 

 are due to the spongy water-holding nature of peat, to its antiseptic 

 property, or to the large amount of decaying organic substance, is quite 

 unknown to me. The Droseras, Utricularias, and Pinguicula seem to 

 depend on the latter quality, and possibly the antiseptic property is 

 responsible for the limited flora, but it is not safe to say more on the 

 subject. 



The effects of a clay and a sandy soil are quite distinct in their 

 extreme forms, but as one finds them under ordinary circumstances it 

 becomes excessively difficult to trace the effect on vegetation in any one 

 field; one may discover typical sand-loving plants in the stony places of 

 an alluvial holm and along the roadsides, where dust and road sweepings 

 are perpetually heaped against the bank, one may find all the clay-loving 

 plants in a sandy district. 



The only habitat which appears to me to be explained by soil is that 

 of Helianthemum vulgare. Its curiously isolated position may con- 



