546 Watson.—Sphagna : Habitats , Adaptations , and Associates. 
1. Species which obtain their mineral substances from the water in 
which they live, have no excessive transpiration or evaporation, but 
supplement their income by the special method. They are usually 
plants of slow growth completely immersed in water. Their acidic 
value is low and their structure is the nearest to the phylogenetically 
primitive form. S. obesum is the best example of this group, but 
some other members of the Subsecunda section approximate to it. 
Species which obtain their mineral substances by excessive transpira¬ 
tion of the redundant water from the exposed chlorophyllous cells, 
and also add to their income by the special method. They are 
plants of constantly moist situations, have a good supply of pendent 
branches for the passage of water to the exposed portions (Fig. 5, A), 
their acidic value is usually low and their chlorophyllous cells have 
been displaced to the outer sides of the leaves. 5 . recurvum and 
vS. amblyphyllum belong to this group, whilst some other allied 
species closely approximate to it. S. squarrosum is better placed 
with this group, though in some respects it approaches the next. 
3. Species which usually obtain most of their mineral substances by 
adsorption of the base and liberation of the acid. They are plants 
of variable habitat, their acidic values are usually high, and their 
structure is greatly modified. The most definite members of this 
group belong to the Acutifolia (e. g. S', rubellmii) and Cymbifolia 
(e. g. S. medium ) sections. They may sometimes be partially 
immersed in acidic water, whilst at other times they are much 
exposed, so that devices protective against dryness are adopted, 
these devices being chiefly for the purposes of facilitating intake 
and passage of water rather than against loss of water. 
Some species have varieties which may be more appropriately placed 
in another group ; thus the variety imbrication of S', squarrosum is nearer to 
the third than to the second group, in which the type may be placed. 
The species of the third group obtain their mineral salts from very 
dilute solutions formed after rain, those of the first group from the dilute 
solutions in which they live (the solids in siliceous streams are often less 
than 0*1 grm. per litre), whilst the second would usually be able to obtain 
a rather stronger solution. The following results were obtained on evapo¬ 
rating the water squeezed out from the tufts of Sphagnum : 
Species. 
Group. 
Habitat of Example tested. 
Solid in Grm. 
per Litre. 
S. cynibifolium 
3 
Moist hollow of heath 
o*o 5 
S. cymbifolium 
3 
Damp hollow of heath 
0*09 
S . Girgensohnii 
3 
Moist places of heath 
0*07 
S. rufescens 
1 
Stream side just above the water, 
a constantly wet place 
o-i 1 
S. subnitens , mixed with 
a little S. cymbifolmm 
3 
' Stream side, but some distance 
above the water 
o*o8 
S. amblyphyllum 
2 
Wet place on heath, a constantly 
moist place 
0-13 
