290 BOTANICAL GAZETTE [OCTOBER 
of course genetic, for the marshes are such soils pulverized and 
leveled by the sea. 
The analyses show further the comparative poverty of the marsh 
soil in lime, certainly the greatest defect of the marshes, and this 
substance is the first which has to be added to degenerating marsh. 
This fact is of much importance ecologically, for to the absence 
of lime is due the possibility of the formation of sphagnum bogs 
so extensively developed with the marshes, the sphagnum not 
growing where lime occurs. The neighboring upland, composed 
of Carboniferous sandstones, also is free from lime. 
The form of occurrence of nitrogen in a soil is very impor- 
tant to its fertility, and as to this the analyses give us no infor- 
mation. The amount of available nitrogen in a soil is closely 
correlated with the presence of bacteria, and here also, for the 
marsh soil, we have no data. The bacterial content is not likely 
to be large, however, since there is so little humus, on which 
they are dependent. 
We must next consider a special phase of soil composition 
very important to our present subject, namely, the presence in it 
of common salt (sodium chlorid) derived from the sea water. 
In minute quantities (small fractions of 1 per cent.) salt in the 
soil, since it has no part in plant nutrition, does not appreciably 
affect vegetation as a whole, though it may influence individual 
forms; but when the percentage rises toward 1 per cent., its 
presence begins to be of consequence, while above I per cent. 
and upwards it produces profound effects upon the form and 
distribution of the vegetation. It acts both chemically and 
physically; chemically in that the plant cannot help absorbing it 
with the water and it affects injuriously some of the vital 
processes," and physically because roots are unable to absorb 
water osmotically (their only method) where more than a very 
small amount of salt is present. With most roots water cannot 
be absorbed at all if it contain as much as 1 per cent. of salt and 
none can absorb it from a solution much, if any, stronger than 3 
per cent. As to the amount of salt contained in the marsh soil, 
3*It can of course do this without acting positively as a poison; to what extent 
the salt is positively poisonous is still uncertain, though the studies of Loeb, True, and 
others seem to show that in some cases it is so 
