320 



work of large iron girders, all of which accounts for its remark- 

 able elasticity and strength. 



These microscopic examinations were commenced in the 

 month of April, when Mr. J. W. Martens of this Club was kind 

 enough to collect some material for me at Lake Mohegan. Dur- 

 ing the summer I had occasion to observe the habit of the plant, 

 especially at Duck Harbor Pond (Wayne Co., Pa.), and in August 

 the microscopic work was finished and the conclusions in regard 

 to the function of the tissue described were reached. Since that 

 time, through the courtesy of Dr. Schenck, of Bonn, I have receiv- 

 ed his " HabiHtationsschrift " " On the Aerenchyma," *etc. In this 

 elaborate paper 34 species of plants mostly tropical, growing in 

 swamps, are described and discussed, all of which produce a tissue, 

 called by Schenck " aerenchyma," identical with, or similar to 

 that of our Nescea, which is also mentioned in an appendix as 

 possessing aerenchyma of the same structure and origin as 

 ssicea, but is not individually described. In the introduction 



Jussicea, but is not individually described. 

 to the article the literature of this tissue is mentioned,! and it 

 appears that as early as 1866 Martins described the " racines 

 aeriferes" of some species of JiissitBa, while in 1888 Scott and 

 Wager gave a full account of the histology and development of 

 this tissue in the floating roots of Sesbania aciileata,. 



As to the function of the tissue Schenck comes to the con- 

 clusion that, as the aerenchyma is produced in plants belonging 

 to widely separated families, but all living under similar con- 

 ditions, it must assume, in all the cases mentioned, the same 

 physiological task ; furthermore, that the aerenchyma is a tissue 

 which facilitates the respiration of plant-organs growing in the 

 water or mud, by furnishing them with oxygen which is trans- 

 mitted from the outside medium through the aerenchyma cells 

 to the interior tissues. After discussing the opinions of some 

 authors that the tissue in question might serve as a floating ap- 

 paratus. Schenck repeats his assertion that a tissue which is 



Pringsheim's Jahrb. xx. pp. 526-574. 

 t CharUs Martins, ,..^xxx\&% racines aeriferes, etc. M6m. Acad. Sc. Montpellier, 

 1866.— S. Rosanoff, ... Schwimm organe von Dcsmanihus natans, Bot. Ztg. 1871. 

 p. 829.— N. Lewakoflsky, Ueber den Einfl. d. Wassers, etc. Ref. Just, lS73, P- 

 594.— K. Perseke. Dissertation, Leipzig i877.-S.:ott and Wager, On the float- 

 ing roots of Sesbania aculcata. Annals. Bot. i. 1888 



