SCIENCE 



Friday, Mat 28, 1915 



CONTENTS 

 Disease Besistance in Plants : De. Otto Appei,. 773 



The Cavern of the Three Brothers: Peofessoe 

 Geoege Grant MacCuedt 782 



Some Earthqualce Phenomena noted in Pan- 

 ama: De. Donald F. MacDonald 783 



The Thomas Say Foundation 784 



Awards of the FranMin Medal 785 



Scientific Notes and News 785 



University and Educational News 790 



Discussion and Correspondence: — 



Zoologists, Teachers and Wild Life Conser- 

 vation: Professor Chas. C. Adams. An 

 Eye Screen for Xfse with the Microscope: 

 Oeton L. Clark. Exhibition of the Royal 

 Photographic Society: Dr. C. E. K. Mees. 790 



Scientific Boolcs: — 



GreenMll's Beport on Gyroscopic Theory: 

 Propessoe D. E. Smith. Bussell on Soil 

 Conditions and Plant Groioth: De. Prank 

 K. Cameron 793 



SharTc Intoxication : Dr. A. H. Clark 795 



Special Articles: — 



The Crown-gall of Alfalfa: De. Oeville T. 

 Wilson. The Food Habits and Distribution 

 of the Texas Horned Lizards: W. M. Win- 

 ton 797 



The American Association for the Advance- 

 ment of Science: — 



Section D — Mechanical Science and Engi- 

 neering : Professor Arthur H. Blanchard. 798 



MSS. intended for publication and books, etc., intended foi 

 review Bbould be aent to Professor J. McKeen Cattell, Garriaon- 

 eo-Hndson, N. Y. 



DISEASE BESISTANCE IN PLANTS^ 

 The control of fungous diseases in plants 

 may be effected in three different ways: (1) 

 By killing- the parasite before it enters the 

 host, (2) by curing the diseased plants, and 

 (3) by growing disease-resistant varieties of 

 cultivated plants or making the susceptible 

 varieties resistant. So far the first method 

 is the one most generally followed, the 

 means employed depending on the nature 

 of the fungus. 



It is easier to protect the host from a 

 fungus which combines a highly developed 

 parasitic character with alternation of 

 hosts than from one which spends its entire 

 life cycle on the same host. For example, 

 when rust {Ecestelia cancellata) appears 

 in a pear orchard the danger from it may be 

 done away with by removing all juniper 

 trees from the neighborhood, the juniper 

 being the host for the alternate stage of the 

 fungus {Gymnosporangium sahinm). The 

 same measure may be adopted in the ease 

 of red rust of wheat {Puccinia graminis) 

 in countries in which the fungus does not 

 reinfect directly the wheat but grows in the 

 spring on the barberry (Berheris). This 

 disease has practically disappeared from 

 Germany since the removal of all barberry 

 and mahonia bushes from the vicinity. 



The destruction of a fungus living on one 

 host only is more difficult because of the 

 fact that this may necessitate the destruc- 

 tion of all diseased plants or parts of them, 

 an undertaking which could hardly be car- 

 ried out completely. However, if carried 



1 A lecture delivered by invitation at the uni- 

 versities of California, Wisconsin, Minnesota and 

 Cornell, and the Iowa Agricultural College, in Oc- 

 tober, 1914. 



