s kind have been investigated among others by
Heraues, Hueppe, and E. Wollny. According to the two first-mentioned
investigators, certain colourless bacteria effect the formation in the
absence of light from humus and carbonates a body resembling in its
nature cellulose.

[60] Investigated by Springer, Gayon and Dupetit, Deherain, and
Marguenne.

APPENDIX TO CHAPTER I.

NOTE I. (p. 68).

The following determinations by Schuebler show the absorptive power of
different kinds of soil-substances. These were obtained by soaking
weighed quantities of the soil in water, and allowing the excess of
liquid to drain away, and weighing the wet earth.

Per cent of water
absorbed by 100
parts of earth.

Siliceous sand 25
Gypsum 27
Calcareous sand 29
Sandy clay 40
Strong clay 50
Arable soil 52
Fine calcareous 85
Garden-earth 89
Humus 190

It has been calculated that the absorptive power of a mixture of
different substances is not simply equal to the sum of their separate
ingredients.

NOTE II. (p. 74).

EVAPORATION.

The retentive property of a soil for water tends to retard evaporation.
The following table by Schuebler shows the rate at which evaporation
proceeds in different soils. The experiment was conducted in the
following way. The soil experimented upon was saturated with water and
spread over a disc, and allowed to evaporate for four hours, when it was
weighed. The amount of time required for the evaporation of 90 per cent
of the water was also estimated. Of 100 parts of water in the wet soil
there evaporated, at 60 deg. Fahr.--

Time required to
In four hours-- evaporate 90 per cent.
From-- per cent. Hours. Minutes.

Quartz 88 4 4
Limestone 76 4 44
Sandy clay 52 5 1
Stiffish clay 46 6 55
Loamy clay 46 7 52
Pure grey clay 32 11 17
Loam 32 11 15
Fine calcium carbonate 28