NOTES OX THE BALD CYPRESS. O 



earthquakes of 1811. Whenever this sinking brought the tops of the 

 cypress knees below the level of the permanent water, the trees all died. 

 The great areas of Reelfoot and the adjacent lakes are still covered by the 

 stately columns of these trees which were killed in this way two thirds of 

 a century ago, and their submerged knees are still traceable, so that there 

 cannot be any doubt of their position ; yet other specimens, in which the 

 knees Avere nearly buried, still survive. 



In various mill-ponds in this district, where artificial flooding of the 

 swamps has brought the permanent level of the water above the top of the 

 knees, the trees have speedily died. This connection between the flooding 

 of the knees and the death of the trees to which they belong is Avell recog- 

 nized by the people of the country. They do not hesitate to determine the 

 height of the summer waters by the altitude of the crests of the knees. 



It seems to me that these facts, — viz., the failure of the knees to develop 

 when the trees grow on high ground; the develojjment of the knees when 

 the roots are in permanent water; the rise of the knees above the perma- 

 nent water level, and to a height varying with that level; and finally, the 

 destruction of the trees whenever the level of i^ermanent water rises above 

 the top of the knees, — incontestablj' show that thei'e is some necessary 

 connection between them and the functions of the roots when the latter 

 are permanently submerged. 



It is not unreasonable to conjecture that this function of the knees is in 

 some way connected with the process of aeration of the sap. It is a well 

 known fact that the roots of most plants are intolerant of continuous im- 

 mersion in water. It seems likely, therefore, that some process connected 

 with the exposure of the sap to the air takes place in these protuberances. 

 This hypothesis is supported by the fact that the knees remain quite vas- 

 cular, and that the process of their growth assures the constant exposure 

 of considerable sm-faces of newly formed bark on the upper part of the 

 knee, a circumstance that would favor the aeration of the sap. The woody 

 part of the knee is also very soft and spongy, ditfering very much from 

 the ordinary wood of the tree. 



It is clear that we have in this tree a singularly variable accommodation 

 to the changeable conditions it encountei's in its ditferent stations ; and the 

 readiness with which the variations are brought about must remain a matr 

 ter of surprise to any one who knows the small amount of flexibility in this 

 respect shown by most of our forest trees. I do not know of another case 



