128 



further that the same Fusarium species (to be described as a new form of 

 Fusarium oxysponim) is capable of producing both the stem canker and 

 wilt diseases, a relationship previously unsuspected. Considerable crown, 

 root and stem rot of greenhouse and field-grown plants was caused by 

 Pythitim ultimum, a new disease of perennial delphiniums. Data have been 

 obtained which make possible a better evaluation of the importance of the 

 fungi and bacteria involved in the delphinium crown rot complex. 



The second lecture by Dr. R. H. Burris, National Research 

 Council Fellov^ in the Department of Botany, Columbia University, 

 v^as on 'Tsotopic Tracers in Biology." The speaker's abstract 

 follows : 



The use of radioactive elements and stable isotopes as tracers has been 

 readily accepted as a promising new approach in the study of biological 

 processes. The general principles of tracing compounds by the incorporation 

 of radioactive atoms or stable atoms of "abnormal" mass, and the determina- 

 tion of radioactivity by the Geiger counter and mass distribution by the 

 mass spectrometer were discussed. 



The stable isotopes of C, N, O, H and S have been concentrated suffi- 

 ciently for use as tracers. Among the radioactive isotopes P, Na, K, As, Fe, 

 Cu and S, have proved especially useful. The short half lives of radioactive C 

 and N limit their applicability. 



Illustrative examples of the application of the stable N^^ isotope to prob- 

 lems in biological nitrogen fixation were cited, and the manner of checking 

 for non-specific exchange reactions was outlined. 



The meeting was adjourned at 4 :40 P.M. to enjoy the tea served 

 by the entertainment committee. 



Respectfully submitted, 



John W. Thomson, Jr. • 

 Recording Secretary 



Minutes of the Meeting on March 4, 1941 



The meeting was called to order at 8:15 P.M. at the American 

 Museum of Natural History by the President, Dr. J. S. Karling. 

 Eighty-six members and guests of the Club were present. 



The minutes of the previous meeting were approved as read. 



Dr. Bold moved. Dr. Bonisteel seconded the motion and the 

 Club voted that the following be admitted by unanimous ballot to 

 membership in the Club : as annual members, Mrs. Wanda K. Farr, 

 American Cyanamid Co., Stamford, Conn. ; as associate member, 

 Mrs. Fitz-Henry Paine, Breeze Hill, Abington, Conn. 



