158 DIRECTION OF DEVELOPMENT. 



handicapped. Seeds of the beech germinate normally, but in the first few 

 years the seedlings show only a weak growth, especially of the aerial parts, as a 

 consequence of the poor soil. Ultimately, the growing roots reach the lower 

 richer soil layers, and the young saplings then begin to stretch upwards. 

 They develop dense thickets in the gaps due to fallen trees, and thus hinder the 

 further development of heath plants. Such forests have mostly a very poor 

 flora, since forest plants lack for nutrients, and heath plants are suppressed 

 by the dense shade. In such places, a complete conversion to heath could 

 occur not at all or only after a long period, since the layer of leached soil must 

 attain such a thickness that the seedlings disappear before their roots reach the 

 deeper nutrient layer. In this event, it is more probable that the beech will 

 be replaced by a tree with lower requirements, such as the pine, before this 

 finally yields to the heath. 



"The formation of 'ortstein' hinders the reproduction of the forest, as soon 

 as the leached layer becomes so thick that frost can not penetrate to its lower 

 limit. At this level, the precipitation of dissolved humus compounds, leached 

 out of the soil above, cements the sand into a humus sandstone. In the heath 

 regions, the latter is laid down for miles as a pure imioterrupted layer at a 

 depth of one foot as a rule. As soon as the 'ortstein' has attained a certain 

 thickness and density, it can not be pierced by plant roots. The latter can 

 penetrate only in small gaps which maintain themselves here and there in the 

 layer. The upper leached layer is thus almost completely separated from the 

 lower nutrient layer. The variations in water content are marked and can 

 no longer be affected by capillarity. As soon as the 'ortstein' begins to develop 

 in the forest, the latter takes on a different look. The roots of beech seedhngs 

 and of young plants of the undergrowth can not penetrate the 'ortstein' and 

 reach the lower soil layer. They languish for a time, and then perish as a 

 consequence of lack of nutrients and water, or of the winter killing of the 

 umipened wood. Undergrowth and reproduction begin to disappear. The 

 gaps produced by the fall of old mature trees are not filled with new growth, 

 and thus afford favorable conditions for heath vegetation. The forest becomes 

 more and more open through the death of old trees, the heath develops cor- 

 respondingly, and soon becomes dominant. After a few decades only isolated 

 trees remain upon the bare field. Elsewhere all is heath. 



"Such are the general features of the process by which the vast stretches of 

 heath have arisen from forest. To-day we have all stages of the development 

 of deciduous wood of beech and oak to typical heath, especially in the eastern 

 transition regions. Conversion to heath is naturally hastened by the clearing 

 and utilization of the forest, though it must occur even without this, through 

 the operation of climatic factors upon sandy soil. 



"The conversion of pine forest into heath is quite similar to that of beech 

 forest, though the lower requirements of the pine enable its seedlings to thrive 

 better in the leached soil. The leaching-out process also proceeds more rapidly 

 owing to the lower nutrient content, but the development of 'ortstein' is less 

 marked. This is due to the fact that the looser canopy of the pine forest, as 

 well as the sparser undergrowth, permits the sun and the wind to hasten 

 decomposition in relation to humus production. On the protected floor of the 

 beech forest, on the contrary, the formation of humus is more marked than 

 decomposition, and there is in consequence a larger supply of humus com- 

 pounds for precipitation as the cement of 'ortstein.' 



"A further method of heath formation is considered by Grebe (1896). In 

 this, the decomposition of the fallen needles or leaves takes place so slowly 

 in dense shady woods, especially of fir and in moist climates, that by far the 



