28 BULLETIN 272, U. S. DEPARTMENT OF AGRICULTURE. 



has been started by the Forest Service in Louisiana to determine 

 what effect the removal of the knees has upon the subsequent growth of 

 the tree. The knees were removed from 15 trees and left on 5 near-by 

 trees to serve as a check for later comparison. It should be noted 

 that other swamp species, including tupelo gum, water ash, white 

 bay, and others, do not produce knees, although they frequently 

 occur in apparently the same situation where cypress has developed 

 knees at least 2 to 5 feet in height. Some of the species do, however, 

 develop slight humps or kinks in the surface roots. 



Although cypress occurs chiefly on the most unstable and treach- 

 erous soils, it is one of the most wmdfirm of all southern commercial 

 trees. 1 On what engineers would pronounce the most dangerous 

 foundation it rears a shaft, often of massive proportions, for 60 to 

 90 feet in height, topped by a wide-spreading head of giant limbs with 

 very numerous branchlets. It is obvious that the wind pressure at 

 times upon a mature cypress is very great. However, Lamborn and 

 Newberry, 2 both of whom traveled extensively in the southern regions, 

 state that they do not recall having seen a living cypress overthrown 

 by the wind. The great resistance offered by cypress to the force of 

 wind is pointed out by Mohr, 3 who visited the path of the severe 

 tropical hurricane of September, 1892, along the Savannah River 

 in Hampton County, South Carolina. He states that "not a single 

 cypress was seen to have yielded to the fury of the storm, although 

 the pines in its track were mowed down like grain before the reaper, 

 and the sturdy live oaks and laurel oaks were uprooted." 



The mass of interwoven horizontal roots, with the aid of hundreds 

 of vertical roots beneath the knees, binds the associated soil materials 

 and furnishes a stable support for the weight of the tree. The large 

 sustaining force of cypress roots is thoroughly recognized by lumber- 

 men and is utilized in the construction of logging railroads over 

 swamps. 



The mechanical function of the knees was pointed out by Lamborn, 4 

 who investigated the subject from the standpoint of a mechanical 

 engineer. In his conclusion he stated "that the most important 

 function of the knees is to stiffen and strengthen the roots, in order 

 that the great tree may anchor itself safely in a yielding material." 

 Mohr in his thorough study of cypress reached the same conclusion. 



In view of the requirements of cypress for an extraordinary root 

 system for support in soft, yielding soils and the binding effect of the 



1 Elliot says: " The cypress resists the violence of our autumnal gales better than any other of our forest 

 trees." Botany of South Carolina and Georgia, p. 643, 1824. 



2 Garden and Forest, Vol. Ill, p. 21. 



s Mohr, Dr. Charles, Manuscript report on cypress, based upon an extensive field study. Forest Service, 

 Department of Agriculture. 



4 Lamborn, Robert H. " The knees of bald cypress: A new explanation of their function." Garden and 

 Forest, Vol. HI, p. 21. 



