400 Scientific Proceedings, Royal Dublin Society. 



if not the ouly, plant, the reaction being close to pH 9. Near Plymouth an 

 embankment carries a road up to and past Stamford Fort. The south side 

 of this embankment was thickly covered with G. ruber. The plant, however, 

 ceased to appear beyond a certain vertical line, save for half a dozen 

 stragglers within ten or twelve feet. Beyond this Achillea Millefolium and 

 Linaria vulgaris were plentiful, also Taraxacum officinale, which occurred in 

 the Ccntrantlius area too. On examining the soil, it was found that the 

 latter was at pH 9'0, and on standing with water for a day it only fell to 

 pH 8-8. It had rather more clay-like particles than had the Achillea region, 

 the reaction of which was no more than pH 8'2. On standing for a day with 

 water this fell to pH 7'6, showing that the amount of carbon dioxide produced 

 by bacteria was not taken up by excess of carbonate, as in the other sample. 

 Evidently one portion of the embankment was made with limestone rubble 

 from Turnchapel quarries, and the other from a slate near its end, which 

 develops a reaction of pH 8-2 or over, and underlies the Middle Devonian 

 Limestone. 



Another point of interest, which, however, requires further work, is the 

 difference in distribution of three species of Convolvulus, all very similar in 

 general habit. C. Soldanella occurs on dunes and sand banks where water 

 is not plentiful ; aeration is very good, and the pH value 8-0-8'4 denotes the 

 bicarbonate region with but little carbon dioxide. C. arvensis occurs in dry 

 situations in fields and on banks, the recorded values being pH 7'6-8'2 ; these 

 are reinforced by experience of other situations not examined. This range 

 denotes bicarbonate with less efficient aeration and more carbon dioxide. 

 Finally, C. Sepium occurs in hedges, in damp thickets, and as a garden weed, 

 the range observed being pPI 7'2-7'8. Tiiis corresponds with, on the average, 

 rather more carbon dioxide than for C. arvensis, namely, with a damper 

 situation. 



Certain heath plants are obviously limited i]i their distribution also ; thus 

 Calluna vtdgaris has been found abundant, at pH 4'6-5'2, on peat or peaty 

 soil. Erica cinerea, however, is found in abundance at pH 4'6-5"4 ; also in 

 drier situations, at pH 5 -4, in earthy soil. Vacciniuvi Myrtillus has the 

 distribution of Calluna rather than of Erica. The limits for sparse occurrence 

 are somewhat wider. 



Agnin, Pieris aquilina is usually found on acid soil; thus, out of ten 

 situations, six were at pH 5-6, three at pH 6-7, and one at pH 7'6. The 

 latter was certainly a spot rich in Pteris, but it was in a gully below land, 

 at pll 6'4, where the plant was abundant. 



In this description, and in the table which follows, dominant means 

 plentiful to the more or less total exclusion of other plants ; abundant means 



