Reaction and Succession in Relation to the Plant Covering . 401 
Water -content. 
Since the mineral particles are fairly uniform as regards the relative 
proportions of the mechanical fractions in the different phases of the dune 
system, the variations in water-content are mainly dependent on the propor- 
tion of organic material present. 
The subjoined table (Table VII), in which the maximum water-content 
is shown, brings out quite clearly how this increases with the increasing age 
of the dune system. 
Table VII. Maximum W ater-contents. 
Dune phase . 
Water by weight . 
0/ 
Water by volume . 
0/ 
> 
Main ridge 
/o 
26.6 
/o 
38-04 
\ 
55 
26.4 
37-75 
55 
24*8 
35-46 
55 
20-3 
29.0 
1 Av. by 
weight 25.4 % 
5 5 
55 
4-3 
34-3 , 
36-1 
r „ 
volume 36.3 % 
„ 
27.6 
39-5 
55 
26-0 
38.0 
5 5 
27-0 
38.6 ’ 
Long Hills 
28*2 
38-0 
55 
28-9 
38.8 
55 
28-9 
38.8 
55 
55 
55 
26.7 
29*0 
32.14 
35-87 
39.88 
43-20 
. Av. by 
>> 
weight 29.46 % 
volume 39.44 % 
55 
3 °- 1 
4°-45 
55 
28-2 
38.00 
55 
31.2 
42.00 
The Hood 
43-9 
55 -oB' 
55 
34-3 
43*94 
55 
34-5 
44.19 
55 
55 
55 
37-3 
29-8 
32-54 
47.80 
38.20 
4 W° 
M Av. by 
>> 
wei g h t 35 - 9 ° % 
volume 45.99 % 
5 5 
33-2 
42-53 
5 » 
3 i -9 
40.86 
,5 
46-59 
59 - 68 , 
Comparing the average water-contents in Table VII with the average 
organic contents already given in Table V, we find that the Long Hills show 
an increased water-content over that of the main ridge of 3-06 per cent., 
whilst the increased water-content of the Hood as compared with the main 
ridge is 10-50. The respective increases in organic content are 0-653 and 2-19. 
If then the increase of the water-content is due almost entirely to the 
increased organic material, it follows that we should be able to calculate 
approximately the increase of water content for the Hood from the organic 
increase, having regard to the figures yielded by the Long Hills. This 
calculated value is 10-26 instead of 10-5 as found experimentally. Put in 
. , . increase of water-content 
another way the ratio 1 ^ § should yield an approxi- 
mcrease of organic content r 
mate constant ; the actual values obtained are 4-68 and 4-79, which are 
as close as could be expected. 
The conclusion seems warranted , then , that the organic material is 
