MOORLAND PLANTS 191 



was the factor in question. In moorland water the difficulty 

 of absorption was supposed to be due to the presence of the 

 large quantities of humus acids, derived chiefly from the 

 dead and partly modified remains of the bog-moss, 

 Sphagnum, present in the peat, acting as toxins and so 

 reducing absorption directly, or rendering minimal absorp- 

 tion necessary as a condition of absorbing small quantities 

 of toxic matter. Dachnowski (1908) has shown that oats 

 and other plants grown in bog water show signs of stunt- 

 ing, particularly in the root system. Treatment with 

 chalk or lamp-black counteracts this effect. His conclusion 

 is that the lowered growth is due to the presence of 

 toxins, chiefly of bacterial origin. Rigg (1916) also found 

 toxic substances in water in which plants had decayed. 

 Burgerstein (1876) had earlier shown that humus extracts 

 reduced transpiration. On the other hand, Montfort (1921) 

 has shown that the passage of water through maize plants 

 — determined by the rate of excretion of water-drops from 

 the leaf tips of the plants in a moist atmosphere — is not 

 diminished when the roots are placed in bog water, but 

 that later on a toxic action sets in. Stocker (1923) has 

 shown that the root system of moor plants is just as 

 extensive related to their aerial organs as that of ordinary 

 mesophytes — that there is no stunting, and that the 

 transpiration for equal weights of root system is greater. 

 His conclusion is that the moor xerophytes are in reality 

 ever-green winter xeroph)rtes, an opinion which had been 

 previously expressed by Gates (19 14). Farmer (19 15) 

 has shown that the specific conductivity of an arborescent 

 heath is only 8 compared with an average figure of 70 

 for broad-leaved trees. The efficiency of the conducting 

 system of the heath must evidently make water economy 

 important. Thatcher (1921) has shown that if a plant is 

 able to produce a healthy root system in peat it transpires 

 in that medium more freely than in ordinary soils, and that 

 it does so at any water content from saturation to the wilting 

 point. She found that healthy root systems were formed 

 by Saltx pentandra , and S. cifierea, Acer pseudoplatanus , and 



