Problem of Xeromorphy in Marsh Plants . 857 
Warming 1 remarks that an insufficient supply of oxygen may obstruct 
respiration, and so depress the functional activity of the roots. The 
researches of Kosaroff, 2 too, show that the absorption of water is retarded 
by suppressing the supply of oxygen to the roots. In this connexion 
it may be noted that the roots of many ‘ dry-marsh plants 5 tend to assume 
a markedly horizontal position, especially when growing in wet peat. This 
is very striking in the case of the tap-roots of certain Umbelliferae. The 
phenomenon may well be correlated with the paucity in oxygen of the 
water-logged soil. 3 
4. The presence of free humus acids. Schimper 4 attributedthe need 
for xeromorphy in the plants of peat-moors to the action of humus acids in 
impeding the absorption of water by the roots. This was accepted by 
Warming and others as ‘ the weightiest cause of the physiological dryness 
of the soil \ 5 But the importance of free humus acids has been disputed by 
Livingston, 6 Transeau, 7 and Dachnowski. 8 Indeed, according to the recent 
important researches of Baumann and Gully, 9 it is extremely doubtful 
whether, in the so-called free humus acids of sour peat soils, we are dealing 
with organic acids at all. These authors attribute the acid character of 
such soils to adsorption by the colloidal cell-walls of plants, especially 
Sphagnum. They produce evidence to show that the cell-walls bring 
about decomposition of salts in solution, a greater proportion of the 
base than of the acid being adsorbed. The acid reaction, then, is due to 
the presence of free hydrogen ions yielded by the acid after the removal 
of the base. 
5. The presence of bog toxins , which act on the roots of plants much 
as do drying media. The existence of such substances in bog water and 
bog soils has been rendered probable by the work of Livingston, 10 and 
later of Dachnowski. 11 These authors published a series of suggestive 
papers from 1904 onwards. They conducted many careful culture experi- 
ments, using polymorphic lower plants as indicators. They both conclude 
that inhibition from bogs of plants other than those possessing xerophytic 
characters is largely due to the presence of these injurious substances, 
which are soluble in water. Dachnowski 12 states that the toxicity of bog 
water can be corrected by various means : e. g. by the addition of certain 
adsorbing agents, and also by aeration. The latter acts, according to him, 
by slowly oxidizing the toxic substances, and not directly on the living roots, 
as supposed by other authors. 
6. The great water-retaining power of peat. Of all soils peat has 
I Warming (’09), p. 195. 2 Kosaroff (’97), quoted by Jost (’07), p. 32. 
3 Yapp (’08), pp. 74-5. 4 Schimper (’03), pp. 15 and m. 
5 Warming, 1. c. 6 Livingston (’05), p. 351. 
7 Transeau (’06), p. 25. 8 Dachnowski (’10), p. 327. 
9 Baumann (’09), and Baumann and Gully (’10). 10 Livingston, 1. c. 
II Dachnowski (’08, ’09, and ’10). 12 Dachnowski (’08), p. 134, &c. 
