1889.] natural sciences of philadelphia. 67 



April 2. 



The President, Dr. Joseph Leidy, in the chair. 



Thirty-nine persons present. 



The production of aerating organs on the roots of swamp and other 

 plants: — The following communication was read from Prof. Wil- 

 liam P. Wilson : — In the winter of 1885-86 I was in South Florida. 

 While studying the plants about Lake Butler in Hillsborough Co., 

 my attention was called to the excrescences on the roots of the bald 

 cypress, Taxodium distichiun Richard, generally called " knees." 

 The water in the lake was very low. During high water the waves 

 had washed bare the roots of many of the cypress trees along the shore. 

 In this way an occasional tree was found whose earlier formed root- 

 system was almost completely exposed. 



These exposed roots offered excellent opportunity for the study of 

 some of the points in the development of the so-called " knees." The 

 very early stages were secured by digging up the complete root- 

 system of young trees which were just beginning to show " knees," 

 and also by cultivating at a later date seedlings under varying 

 conditions. Some of the results early obtained led to the growing: of 

 other plants under varying conditions of moisture and dryness. 



Certain points concerning the development and function of roots 

 under the influence of excessive moisture, which seem to be clearly 

 made out, will be very briefly stated in this paper. A more extended 

 discussion of the same subject, including the anatomy of some of the 

 roots with explanatory cuts will, I hope, soon follow in the Proceed- 

 ings of this Academy. 



Taxodium distichum produces whenever it grows in wet places, 

 excrescences on its roots called " knees." These knees vary in size, 

 in height and in number in accordance with the depth of water 

 or amount of moisture existing under the trees. When the water 

 for a part of the year is deep the knees grow correspondingly high. If 

 the ground is simply overflowed and kept saturated with moisture 

 most of the season these knees grow low but multiply themselves in 

 great numbers. Fifty to one hundred may be produced from the root- 

 system of one tree. If the overflow is considerable in depth the 

 knees may exceed eight or ten feet in height. They are strictly root 

 productions as will be shown later both by their development and 

 anatomy. 



The development of these knees is by two very distinct methods. 

 First, if the seed germinates and the plant begins its growth in a 

 very wet place, many of the small roots which are only six or eight 

 inches below the soil grow upward towards the surface at slightly 

 varying angles of from 20° to 35°. Upon reaching the surface these 

 same roots turn and go down into the soil at about the same angle. 

 Some of them may, if the soil is very wet, or if under the water for 



