370 



SCIENCE 



[Vol. LVI, No. 1448 



theory is obviously incomplete. As he so ap- 

 positely puts the ease himself: "We all have 

 partially permeable intellects." 



At this stage, indeed, it is altogether pre- 

 mature to express an opinion as to the outcome 

 of the struggle. What is certain is that Loeb 

 has made, in this volume, a brilliant thrust 

 which his adversaries will find it difficult to 

 counter. There are many points of detail 

 in his experimental work which will curdle 

 the .blood of any analytical chemist, yet it ap- 

 pears on close examination that the errors in- 

 troduced are, after all, insufficient to affect 

 the main issue. The opponents of Loeib's views, 

 in any case, cannot restrict themselves to at- 

 tacking the weak points of his presentation; 

 he has already succeeded so far as to put them 

 definitely on the defensive. To quote from 

 his own preface: "Any rival theory (of col- 

 loidal behavior) which is intended to replace 

 the Donnan theory must be able to accomplisli 

 at least as much as the Donnan theory, i. e., 

 it must give a quantitative, mathematical and 

 rationalistic explanation of the curves express- 

 ing the infiuence of hydrogen ion concentra- 

 tion, valency of ions, and concentration of 

 electrolytes on colloidal behavior; and it must 

 explain these curves not for one property 

 alone but for all the properties, electrical 

 charges, osmotic pressure, swelling, viscosity, 

 and stability of solution, since all these 

 properties are affected by electrolytes in a 

 similar way." 



This quotation may be supplemented by an- 

 other, from the- final page of the book, in- 

 dicating the importance of Loeb's work out- 

 side of chemistry. "If Donnan's theory of 

 membrane equilibria furnishes the mathematic- 

 al and quantitative basis for a theory of col- 

 loidal behavior of the proteins, as the writer 

 believes it does, it may be predicted that this 

 theory will become one of the foundations 

 upon which modern physiology will have to 

 rest." 



Every so-called colloidal chemist will evi- 

 dently be forced to read Loeb's book in self- 

 defense. Those also who are only indirectly 

 interested in colloidal phenomena cannot fail 

 to find it stimulating. 



James Kendall 



SPECIAL ARTICLES 



MOSAIC CROSS-INOCULATION AND INSECT 

 TRANSMISSION STUDIES 



Whether or not the plant disease known as 

 mosaic is transmissible to plants of different 

 orders, and the role of insects as agents in 

 such transmission, are questions of funda- 

 mental importance. It is generally held that 

 mosaic of the Cucurbitacese, Solanaceae and 

 Leguminacsffl are all qiiite specific and with few 

 exceptions transmissible only to species within 

 the same family. Certain mosaic diseases have 

 been described indicating that even among spe- 

 cies within the same family there may be two 

 or more types of the disease. Allard^ in 1916 

 described a specific mosaic disease on Nicotiana 

 viscosum distinct from the mosaic disease of 

 Nicotiana tabacum. Jagger--^ in 1917 and 

 1918 reports three specific mosaic diseases of 

 the cucurbits. The tendency has thus been to 

 divide mosaic into types which are distinct in 

 their host range. 



As opposed to the evidence indicating that 

 there are a number of types of mosaic which 

 are specific to a narrow host range, we have 

 evidence showing that mosaic will cross to 

 species belonging to other families and orders. 

 Jagger* in 1918 published results of cross- 

 inoculation studies where he succeeded in trans- 

 ferring mosaic from the CucurbitaceEB to spe- 

 cies of two other families of the Order Campa- 

 nulales. Doolittle^ has shown that mosaic of 

 cucumber is transmissible to Martynia louisi- 

 ana, a species belonging to the Order Polemo- 

 niales. 



Cross-inoculation experiments by the writer 

 have shown that the mosaic diseases of the 

 CucurbitacesB, Solanacese and Leguminaceae are 

 inter-transmissible. Four petunia plants inocu- 

 lated with mosaic from crookneck squash be- 

 came infected while an equal number of checks 

 remained healthy. The inoculations were made 

 by inserting mosaic tissue into the stem with a 

 sterile scalpel. An experiment in which juice 

 from mosaic plants was inoculated hypo- 



T-Journ. Agr. Research, 7: 481-486, 1916. 

 ^Phytopathology, 7: 61, 1917. 

 s Phytopathology, 8: 74-75, 1918. 

 i Phytopathology, S: 32-33, 1918. 

 6 U. S. D. A. Bull. 879, 1-69, 1920. 



