24t) 



meter high. Poverty in nutritive substances in combination with the lack of 

 moisture, easily becoming great in lead sand, are the causes of an ultimate 

 blighting at the tops. 



Figure 30 shows the root growth of an oak. Tiic oak was planted after 

 the layer of swamp ore had been broken through artificially. But this layer 

 of swamp ore had later re-united and the portion of the root in g, nearly 

 shut away from an air supply, had practically stopped growing. No mycor- 

 rhiza, or scarcely any, could be found on this part of the root. 



Graebner attaches the fol- 

 lowing significance to such 

 phenomena. If the swamp 

 ore is deposited below the 

 roots, the earth lying above it 

 is naturally exposed to great 

 fluctuations in moisture, and 

 in times of drought becomes 

 so dry that the plants die from 

 a lack of moisture. In cases 

 of this kind, however, the 

 plants forming their roots en- 

 tirely in the lead sand, exhibit 

 a very weak growth, grad- 

 ually making itself evident by 

 short, yellow needles. If the 

 swamp ore, however, lies di- 

 rectly around the roots, which 

 are about as large as knitting 

 needles, and have penetrated 

 in to the better soil, it presses 

 against them, causing knotty 

 swellings. This takes place if 

 the roots reach the better sub- 

 soil through an opening in the 

 swamp ore layer. Such me- 

 chanical constrictions disturb 

 further root growth. The tree 

 is therefore essentially dependent on the roots lying above the swamp ore 

 layer. Growth and vital activity are normal during the spring dampness, but 

 all activity stops if a hot summer dries out the soil. Graebner found the root 

 tips shrivelling, turning to resin or dying entirely. In larger trees, with a 

 renewal of moisture, time and material are necessary for new root growth. 

 This loss in time and substance becomes evident in the growth of the aerial 

 axis and, in combination with the results of the period of drought, causes in 

 great part the weak growth of the moor pines. The plantations improve as 

 soon as the fluctuations of moisture are less extreme. 



Fig- 29. "A meadow ore pine" from the Liine- 

 burg-er moor, grown after the formation of the 

 meadow ore. 



r raw humus, b lead sand, o meadow ore. Below the meadow 

 ore the yellow sand begins. (After Graebner.) 



