346 МК. В. S. ADAMSON : АХ ECOLOGICAL STUDY 
is very deep down, as in the desert soils studied by Livingston * t, but in 
these soils the water-table in winter rises almost or quite to the surface, when 
the soil becomes supersaturated with water. — Indeed, in parts of the 
'aleareous clay the water-table is only about 8—6 inches below the surface 
at the beginning of the growing season, unless the conditions have been very 
dry. In summer the water-holding capacity becomes of much greater 
importance as the water-table sinks lower and lower, and, indeed, in. some 
of the more sandy parts of the loam, where it is only about 36 per cent., the 
soil near the surface may get very dry. 
As a whole the calcareous clay soil shows a higher water-content than 
those of the loam, the difference being especially pronounced in summer. 
The average content for the year for the marl is 39:8 per cent., and for the 
loam 18:2. These annual average contents, however, do not give much 
idea of the conditions under which the plants grow, the essential points 
being the water present at the eritical period, or period of most rapid 
growth *. The details, however, will be considered later in relation to the 
conditions they affect. 
With regard to the ratio of water-content to humus, that for the calcareous 
clay works out at 2*6 and for the loam 2:9. These figures are higher than 
might have been expected, owing to the poorness of these caleareous soils in 
humus f. 
Experiments have been carried out to try and obtain the amount of 
available water or chresard $. The method advocated by Clements is 
extremely difficult in practice, especially in removing a block of earth round 
the roots of the plant without either damaging the roots or considerably 
upsetting the plant. Experiments, however, were carried out with Mercurialis 
perennis with the result :— 
Holard $... 384 per cent. 
Echard $... 126 „no ,, 
Chresard... 258 „оз 
Average figures as result 
j of several experiments. 
These agree fairly closely with the figures for a clay soil obtained by 
Hedgecock |, who used saturated soil as a holard and mesophytie species. 
His figures are for clay :— 
Holard ......... MM 41:4 per cent. 
Берата н T3 „у 
Chresard ............. Qo Т, y 
* Livingston, 1910, p. 252. + Livingston, 1906, p. 16. | Cf. Moss, 1907, p. 52, 
$ Clements, 1905, p. 32. || Hedgecock, 1902, 
