270 Plant Distribution and Basic Ratios. 
fied. The process of leaching, from which originates soil 
sourness, is not one which acts on all the soil bases at the same 
rate. Analysis of drainage or of natural surface waters shew 
that lime (calcium) salts are removed most rapidly, potassium 
(and to a less extent sodium) most slowly. Leaching should 
therefore result in potassium and sodium becoming pre- 
dominant in the soil complex rather than calcium (or mag- 
nesium). The accumulation of organic matter which usually 
accompanies leaching should lead to the same result, since 
these soil colloids absorb potassium (and sodium) more rapidly 
than calcium and magnesium. It seems, therefore, that sour 
soils are characterised normally by a high ratio of potassium 
and sodium to calcium and magnesium — a ratio which, for 
the sake of brevity, may be called the basic ratio. 
The plants growing in sour soils are remarkable for the 
presence of large quantities of fats. Upon the basic ratio 
of the soil must depend, to a considerable extent, the mobility 
of the fats in the plant, for the ease with which substances 
are moved in or out of the living protoplasm of a cell is known 
to depend very largely upon the basic ratio. Such a movement 
is generally favoured by a high basic ratio, largely owing to 
the effect of the ratio upon the fats in the outer layers of 
protoplasm. Moreover, if potassium and sodium predominate,, 
the fats form soluble and easily diffusible soaps which can be 
moved to all parts of the plant. If calcium is abundant, 
however, insoluble calcium soaps are formed, and the roots 
tend to become coated by an impervious layer of fatty origin, 
and unable, therefore, to carry on their absorptive function. 
The distribution of fats in roots has been modified along 
these lines by Miss E. Bentley and Prof. J. H. Priestley. 
It seems therefore clear that a high basic ratio is a favourable 
factor in the growth of moor and heath plants. 
The abundance of mobile fats in these plants is doubtless 
also important, since it accounts for the thickness of their 
cuticle and for several features of internal structure. It may 
explain also their .slow growth. Since the presence of fatty 
acids is associated with the possibility of splitting off carbon 
dioxide in the absence of oxygen, we may account for the fact 
that these plants live in soils which are often deficient in 
oxygen. 
It is curious that a similar group of factors seems to be 
operating in the case of the unicellular free floating algae 
(plankton) for fresh water lakes. Generally speaking, those 
algae which produce much fat (e.g., Diatoms, Ceratium 
Mrundinella) are characteristic of calcareous water (basic 
ratio low). In fresh waters with a high basic ratio, green 
algae, producing chiefly starch, are predominant. While 
most Desmids belong to this latter group — a few produce 
Naturalist 
