192 



of Taxodium distichum and of Finns serotina which arc not formed on dry 

 soils, and are described by Wilson' as aerating organs. 



An example of the injury to vegetation, due to a direct deposition of 

 silt, is furnished by Robinet- of Toulouse, where the nurseries had stood 

 for only two days under water. At the base of some plants very little mud 

 was deposited. These remained healthy. But when the mud covered the base 

 of their trunks, possibly 10 to 12 cm. deep, the damage was great. Almond, 

 acacia, cherry (even the mahaleb cherry) mountain ash, Tigustrum, Ma- 

 honia, Evonymous and most conifers were killed. Individual specimens of 

 Crataegus, Pirus Communis (of which those grafted on the quince suffer 

 less) Pirus Mains, Castanea, Mespilus, Catalpa, etc., which had stood 8 to 

 10 days under water, blackened at the base and died when the silt was not 

 removed. Platanus. Alnus, Ulmus did not suffer, and Populus, as well as 

 Salix (weeping willow) . developed many roots from the base of the trunk out 

 into the silt. All the specimens of Sophora, Fraxinus, Carpinus, Fagus, 

 Betula and Robinia did not die ; the leaves of the survivors, however, turned 

 yelloiv. The linden and chestnut lost all their leaves. Evergreen plants, 

 and even a part of the conifers, lost their leaves wh^n they had been covered 

 by water. 



Of double importance is this change in the physical constitution of the 

 soil in regions exposed to frequent inundations and, among them, the soils 

 suffer most which are flooded by sea water. Aside from the injury to vege- 

 tation from the large salt content of the soil, there is found, according to 

 A. Maycr\ as a resulting phenomenon of a dense covering, noticeable at 

 times only in the second year, a formation of a black layer, strongly im- 

 pregnated with iron sulfate, which may further injure vegetation. 



Von Gohren* also emphasizes the formation of such kinds of ferrugi- 

 nous layers called "Knick" in West Friesland in very humus, loamy and 

 clayey mud deposits of sea and river marshes and explains their production 

 by the fact that the ferric oxid in the loam is reduced to ferrous oxid by 

 the organic substances in the absence of air. This ferrous oxid combines 

 with the crenate acid to form crenic ferrous oxid. Crenic ferrous oxid, 

 distributed in ever\'^ direction, is gradually oxidized again, cements together 

 all parts of the soil as ferric hydroxid and co-operates in the formation of 

 meadow ore of such ill-repute. We will finish considering the formation of 

 meadow ore when discussing the peculiarities of swamp soil and now turn 

 first to the phenomena of silt covering under the influence of salt solutions 

 found in the use of fcriUizinij salts. 



Mayer's experiments show that particles of clay suspended in water 

 are precipitated dift'erently when they are in suspension in pure water or in 

 water containing sodium chlorid and other admixtures. In pure water 



1 Wilson, W. P. The ])roductioii of aerating organs on the roots of swamp and 

 other plants; cit. Bot. Jahre.sber. 1889, I, p. 682. 



- Revue horticole; cit. Wiener Obst- u. Gartenzeitung 1876, p. 37. 



3 Mayer, A., Ueber die Einwirkung von Salzlosungen auf die Absetzungsver- 

 haltnisse toniger Erden. (Forsch. auf dem Gebicte d. Agrik.- Physik. 1879, p. 251.) 



* von Gohren; Boden und Atmosphiire. Leipzig 1877, p. 56. 



