92 



1). Growth of Stilts. 



(i'.r.KVATIOX OF THE RoOTS OF TrEKS. ) 



In this connection it is advisable to consider still more closely the fact 

 that large forest trees grow with their older root branches above the ground, 

 so that the base of the stem is carried on a number of stilts. This position 

 gives scantier anchorage to the trees and results disadvantageously since 

 they are more easily blown down in wind storms. In addition to this there 

 is a smaller provision of water and the roots are peculiarly sensitive. 



These stilted growths form two types ; first, in spruces, where the base 

 of the trunk is raised high above the soil and the strong branches of the 

 root crown have never been below the top of the earth ; second, in pines, not 

 rare on strongly undulating sandy soil, in which the base of the trunk has 

 previously been covered with soil or may even frequently rest on its surface 

 so that part of the crown is covered with earth, while the other part 

 has been uncovered by the washing away of the soil. In extreme cases 

 the soil slides out from under the trunk so that the whole tree stands on 

 stilts. 



Examples of the first type are described and illustrated by L. Klein^ 

 (Figure 4). He explains the production of the phenomenon as follows: — 

 If spruces or firs have been felled in the mountains a stump is left 

 standing which weathers gradually on its upper surface and becomes 

 covered with moss. Later Vaccinia etc. infest this moss cushion beneath 

 which is produced a thin humus layer. If self-sown spruces or firs begin to 

 grow on the moss-covered surface of the stump, the little young growing 

 roots creep under the moss-covering in all directions over the surface of the 

 stump and then down its sides to the soil, and develop further there, like every 

 other root. In the course of many decades the roots become stronger, the old 

 stump slowly rots away. Klein answers the question, as to why one usually 

 finds spruces much more rarely than firs and never any deciduous trees with 

 this stilt-like growth, when he states that the water needed by deciduous 

 trees is possibly ten times as great as that of conifers and that on this ac- 

 count the seedling of a deciduous tree would not find enough water perma- 

 nently on the surface of the stump for its development. I'-ven if deciduous 

 trees do not grow on stilts, yet similar structures such as the sheath growth, 

 may nevertheless be found. This occurs especially in willows. Where old 

 willows grow along country roads, one finds at times the appearance of a 

 new trunk growing independently out of the decayed heart of the hollow 

 old trunk, so that the woody cylinder of the old trunk surrounds the young 

 tree like a wide sheath. Such cases are easily explained in the pollarded 

 willows when the crown is entirely cut off every year or every second year, in 

 order to obtain as many young shoots as possible. With the rapid rotting of 

 willow-wood on large pollarded surfaces, soil accumulates very quickly from 



1 Klein, L,., Die botanischen Naturdenkmiiler des Grofsherzogtums Baden u. ihre 

 Erhaltung-. Festrede. Karlsruhe 190-1, p. 13, Fig. 7. 



