January 8, 1890.] 



Garden and Forest. 



21 



C. vestita is also a deciduous species of great beauty, and, 

 like C. Veitchii, is exceedingly valuable for cutting. It has large, 

 squarish, silvery gray pseudo-bulbs and broadly lanceolate 

 nervose leaves, with tall, gracefully arched scapes of creamy 

 white flowers, with a rich colored spot on the base of the lip. 

 There are often twenty-four and more of these beautiful flow- 

 ers on a spike. These plants occupy a very small space, and 

 every lover of Orchids should have a few of each kind. There 

 is generally a fine display in our show-house at this season 

 with these flowers, and some Maiden-hair Ferns intermixed 

 with them. 



Staatsburgh-on-Hudson, N.Y. F. Atkins. 



Correspondence. 



The Knees of the Bald Cypress ; A New Theory 



of Their Function. 

 To the Editor of Garden and Forest : 



Sir. — From time to time, during and since my first visit to 

 our southern tier of states in 1876, I have examined, sketched 

 and photographed the roots of the Deciduous Cypress — the 

 Taxodium distichum of Richard. I was attracted to the tree 

 because of the singular beauty of its form and foliage and by 

 the unusual boldness with which it raises its great, gray, 

 smooth column, sometimes over a hundred feet, perpendic- 

 ularly, above and upon what an engineer would pronounce a 

 most dangerous foundation — loose submerged sand, the satu- 

 rated morass or the soft alluvium of low river margins.* But 

 notwithstanding this seeming insecurity, I have never found 

 a healthy Cypress that had fallen before the fierce hurricanes 

 that sweep through the southern forest-lands. f 



The surprising and characteristic temerity of the tree is 

 accompanied by another striking peculiarity — it almost in- 

 variably, in soft soils, throws upward from the upper surface 

 of its roots conspicuous protuberances that are known as 

 "Cypress knees." ;]; 



These seemingly abnormal growths have attracted much 

 attention, and for more than half a century have furnished an 

 enigma to the solution of which scientific travelers have 

 addressed themselves. Michaux made a careful study of the 

 Cypresses, and in his " Sylva," published in 1819, says: "The 

 roots are charged with protuberances eighteen to twenty-four 

 inches high. \ These protuberances are always hollow, and 

 smooth on the surface, and are covered with a reddish bark, 

 like the roots, which they resemble in softness of wood. They 

 exhibit no sign of vegetation, and I have never succeeded in 

 obtaining shoots by wounding the surface and covering it with 

 earth. They are peculiar to the Cypress, and begin to ap- 

 pear when it is twenty to twenty-five feet. high." Michaux 

 adds, with the frankness natural to a scientific mind, " No 

 cause can be assigned for their existence." Hoopes says 

 in his " Book of Evergreens" (1868) : " No apparent func- 

 tion for which the knees are adapted has been ascertained." 

 And Veitch, who seems to have studied the protuberances 

 in England, gives in his "Manual" (1881, p. 216) a picture of 

 a tree growing at Ilesworth, surrounded by scores of knees, 

 and says : " They are peculiar to this Cypress and no cause 

 has been assigned for their existence." That the question 

 continued in this unilluminated condition until recently, was 

 shown in 1882, when I had the privilege of visiting, in com- 

 pany with the highest botanical authorities, Dr. Gray, Thomas 



* It is a pleasure to follow Bartram in his enthusiastic burst of admiration for 

 tli is tree as he writes of it in east Florida u6 years ago: "This Cypress is in the first 

 order ol North American trees. Its majestic stature is surprising. On approach- 

 ing it we are struck with a kind of awe at beholding the stntehness of its trunk-. 

 lifting its cumbrous top toward the skies and casting a wide shade on the ground 

 as a dark intervening cloud, which from time to time excludes the rays of the sun. 

 The delicacy of its color and the texture of its leaves exceed everything in vege- 

 tation. . . . Prodigious buttresses branch from the tr link on every side, each of 

 which terminates underground in a very large, strong, serpentine root, which 

 strikes off and branches every way just under the surface of the earth, and from 

 these roots grow woody cones, called Cypress knees, four, five and six feet high 

 and from six to eighteen inches and two feet in diameter at the base. 



t Elliot ("Bot. of S. C. and Ga.," 1824, p. 6.(3) says: "This Cypress resists the 

 violence of our autumnal gales better than any other of our forest trees." Bv my 

 friend. Dr. J. S. Newberry, whose extended geological labors have led him to 

 examine manv widely separated Cypress-bearing regions in the Mississippi Val- 

 ley and elsewhere, 1 am assured that lie remembers no instance of the overthrow 

 by the wind of a living T. distichum. 



X Professor Wilson, who has made a careful and valuable study of the species in 

 the forests of southern Florida, and also by cultivation, writes, regarding the forma- 

 tion of these protuberances, " The small roots, which are six or eighl inches below 

 the surface, grow upward," . . . "and, upon reaching the surface, turn and go 

 down into the soil;". . . " at each point where the root comes to the surface, be- 

 gins later the development, on its upper side, of the so-called 'knees '" — Proc. 

 Acad. Nat. Sci., Philadelphia, April, 1889. In the organ of the Pennsylvania Forest 

 Association. Forest Leaves (December, 1889), is an excellent article bv Professor 

 Wilson on the T. distichum and a remarkably fine engraving of a tree with enor- 

 mous knees. 



§ I have ridden among them in central Florida in temporarily dry upland basins, 

 where they arose to my breast as I sat upon the saddle, and were not less than 

 seven feet in height above the root. 



Meehan, John H. Redfield, John Ball, Professor Carruthers 

 and others, the classic collection of trees planted by William 

 Bartram on the borders of the Schuylkill. There we examined 

 a fine Cypress and the knees it had produced. Dr. Gray then 

 told me that the use to the tree of the knees was unknown. 

 I remarked that they might be a means of raising a point on 

 the root above surrounding water to the end that a leaf-bearing 

 shoot could readily sprout therefrom. To this suggestion he 

 made the same statement made by Michaux and above re- 

 corded. Unaware that the subject had been so thoroughly 

 investigated, I have since that period examined hundreds of 

 living "knees" in southern swamps, and found upon them 

 no trace of bud, leaf or sprout, except where some seed may 

 have lodged in a decayed or depressed portion of the surface 

 and there taken root. 



In 1887 I had the good fortune to find a number of Cypress- 

 trees under such unusual conditions that their aforetime 

 subterranean anatomy could be studied without obstruction, 

 and I reached a conclusion respecting the use to the tree of 

 the protuberances, which I have retained in my note-book, 

 awaiting an opportunity to make some further illustrative 

 sketches before placing it before botanists. Some recent publi- 

 cations on the subject, by widely and favorably known authors, 

 have, however, ascribed to the Cypress-knees the sole function 

 of aerating the sap of the parent tree, and this idea bids fair to 

 become embedded in botanical literature. Therefore this com- 

 munication comes to you earlier than I had purposed sending it. 



Stretches of the shore of Lake Monroe, in central Florida, 

 are closely set with large Cypress-trees. They grow in various 

 kinds of bottom — clay, mud and sand. Those of which I shall 

 here speak stood in sand so loose that when the level of the 

 water was lowered the waves readily washed it away and car- 

 ried it into the depths of the lake. Some four vertical feet of 

 the root-system was thus finely exposed. After several days 

 spent in examining a score or more large trees that had been 

 thus denuded I became convinced that the most important 

 function of the Cypress knee is to stiffen and strengthen the 

 root, in order that a great tree may anchor itself safely in a 

 yielding material. 



The word "anchor" is indeed an apt one here, for the liv- 

 ing root, curved to its work and firmly grasping the sandy 

 bottom, suggests vividly the best bower-anchor that a man- 

 of-war may throw into similar loose sands, when threatened 

 by the very atmospheric forces that the Taxodium has been 

 fitting itself to resist since Tertiary times.* 



Truly a most admirable and economical arrangement to 

 stiffen and strengthen the connection between the shank of 

 the anchor and its' fluke is this knee, and usually in the living 

 anchor the fluke branches or broadens as it descends, so that 

 its effectiveness is greatly increased, like the sailor's anchor 

 of many flukes, or the " mushroom anchor " that he may 

 have learned to depend upon where the bottom is softest. 



Theaccompanying picture (see p. 20) isfrom a photograph that 

 I made in 1887 of the lower portion of a tree that rises some sev- 

 enty feet above the shore line of Lake Monroe. The original 

 surface of the sand was near the level of the higher roots. The 

 picture shows the manner in which this peculiarspecies throws 

 out horizontal roots from its conical (usually hollow) buttressed 

 base. At different distances from this conical base these hor- 

 izontal roots project strong branches more or less perpendicu- 

 larly into the earth. Where such perpendicular "flukes" 

 branch from the main horizontal "shank," it will be seen, 

 there is formed a large knob, which is the "knee " under dis- 

 cussion. This knee, when fully developed, is generally hol- 

 low, f comparatively soft, gnarled, and very difficult to rupture, 

 so that it has the quality of a spring that becomes more rigid 

 as it is extended or compressed out of its normal shape. 

 When in a hurricane the great tree rocks back and forth on 

 its base, and with its immense leverage pulls upon this odd 

 shaped wooden anchor, instead of straightening out in the solt 

 material, as an ordinary root might; thus allowing the tree 

 to lean over and add its weight to the destructive force of the 

 storm, it grips the sand as the bower-anchor would do, and 

 resists every motion. The elasticity at the point of junction 

 allows one after another of the perpendicular flukes attached 

 to the same shank to come into effective action, so that before 



* Professor Shaler, in a most interesting treatise on the nature and associations 



of '/'. distichum, shows that the Cypress which existed in the Miocene age has 



'nee then probably urndually changed its habitat from the dTier ground to the 



vamp areas. Pee Mem Museum Comp. Zoology, Harvard Univ., Vol. XVI., No. i. 



swamp ; 



t My friend Thomas Meehan in Foi ins me [December 17th, 1880I that he has 

 served a case where the interior hollow makes an annual layer of hark equally 

 with the exterior " and he is of the opinion that " it is bv the decay of the outer 

 layer of this inside course of bark after several years that the knob becomes, hol- 

 low." If this habit is general it is an admirable means of forming and of preserv- 

 ing undecayed, at the smallest cost to the tree, a living elastic sli engthener at the 

 forking of the roots. 



oh 



