SCIENCE 



Friday, April 2, 1915 



CONTENTS 

 Mycology in Belation to Phytopathology : De. 

 C. L. Shear 479 



Edward Weston's Inventions: Dk. Leo Baeke- 

 LAND 484 



Note on the Orbits of Freely Falling Bodies: 

 Pkesident E. S. "Woodward 492 



Arthur von Auwers : Professor E. G. Aitken. 495 



Scientific Notes and News 497 



and Educational News 501 



Discussion and Correspondence: — 



The Origin of Human Twins from a Single 

 Ovum: Mabgaret V. Cobb. Naturalist's 

 Directory : S. E. Cassino 501 



Scientific BooTcs: — 

 Kleb's Variolation im achtzehnten Jahrhun- 

 dert: Dr. F. H. Garrison. Shodes's 

 Primer on Alternating Currents; Barr and 

 Archibald on Alternating-Current Ma- 

 chinery: Professor Ealph E. Lawrence. 502 



Scientific Journals and Articles 505 



Special Articles: — 

 Interpolation as a Means of Approximation 

 to the Gamma Function for Sigh Values 

 of n^ : Eaymond Pearl 506 



The Geological Society of America: Dr. Ed- 

 mund Otis Hoyet 507 



MSB. intended for publication and books, etc., intended for 

 reyiew should be sent to Professor J. McEeen Cattell, Girrison- 

 On-Hudson, N. Y. 



MYCOLOGY IN BELATION TO PBYTOPA- 

 THOLOGYi 



In preparing a presidential address one 

 has always to meet and answer the same 

 old question that has confronted presi- 

 dents and retiring presidents of societies 

 ever since pi'esidents and presidential ad- 

 dresses were invented, i. e., Should the 

 effort be primarily to entertain and amuse, 

 or to instruct? I fear that any effort of 

 mine to entertain would be a grievous fail- 

 ure, while an effort to instruct may be but 

 little more successful. Since of two evils 

 we are advised to choose the lesser, I have 

 decided to attempt something more in the 

 line of instruction than entertainment. 

 Instruction is usually regarded, I believe, 

 as a more or less normal function of a. 

 specialist, and as modern social and eco- 

 nomic conditions have compelled specializa- 

 tion, we must accept the consequence. 



The subject of plant pathology properly 

 includes all the phenomena connected with 

 abnormal forms and functions of plants. 

 These abnormal conditions may be grouped 

 in three classes, according to their origin: 

 First, those which are of non-parasitic 

 origin; second, those which are caused by 

 plant parasites; third, those which are 

 caused by animals. Excluding from pres- 

 ent consideration diseases directly due to 

 animals, we have left the two classes, non- 

 parasitic and parasitic. By far the greater 

 part of the trouble with which the phyto- 

 pathologist has to deal are caused by plant 

 parasites. In fact, the greater part of the 

 phytopathology of to-day might quite 

 properly be designated parasitology, and 



1 Address of the retiring president of the Bo- 

 tanical Society of Washington, March 2, 1915. 



