Septembee 7, 1917] 



SCIENCE 



243 



in the complete solution and dissolution of 

 the cell. Photogenin is a colloid and I would 

 suggest that these substances have a similar 

 action on the colloidal particles of photogenin. 

 We are not dealing here with a cytolysis of 

 cell fragments present in the secretion, since 

 these cytolytic agents (salts, thymol, etc.) 

 cause light production even in solutions of 

 photogenin filtered through porcelain or sili- 

 ceous filters which remove all granules and 

 cell fragments. I would suggest, therefore, as 

 a working hypothesis rather than a formal 

 theory, that photophelein acts by changing the 

 aggregation state of the colloidal particles of 

 photogenin toward that of greater disi>ersion, 

 thus increasing the surface of the particles. 

 It is known that oxidation occurs at the sur- 

 face of many colloidal particles, and light pro- 

 duction might easily result from auto-oxida- 

 tion accompanying the dispersion of the col- 

 loidal particles. 



Photopheleins from different species of ani- 

 mals have different chemical properties and, 

 like the cytolysins, they are also specific to a 

 considerable degree. Firefly photophelein will 

 produce light on mixing with photogenin of 

 other insects (Pyrophorus) , but none or very 

 faint light on mixing with photogenin from 

 Cypndina. A non-luminous species of Cyp- 

 ridina- contains a photophelein with marked 

 light-producing action on the photogenin of the 

 luminous Cypridina, but none with firefly 

 photogenin. Photophelein, therefore, is to be 

 compared with the specific cytolytic substances 

 of blood sera, with this exception, that it is 

 the photophelein of the same species which 

 has the greatest light producing action whereas 

 the blood of the foreign species is the one 

 possessing the greatest cytolytic (hemolytic) 

 power. 



E. Newton "FTarvey 



Princeton University 



inoculations on ribes with cronar- 

 tium ribicola fischers 



The white pine blister rust is established 

 in. the native white pine growth of many parts 



1 Published by permission of the Secretary of 

 Agriculture. 



of New England. Since, in most sections of 

 New England, the pine far outvalues the cul- 

 tivated currants and gooseberries, the latter, 

 together with the wild Rites, are being re- 

 moved to hold the disease under control. A 

 cultivated currant or gooseberry, not suscep- 

 tible to the disease and possessing commercial 

 qualities, would be of much practical impor- 

 tance for future planting within the diseased 

 area. Even a wild species of Ribes immune 

 to the disease might be of value for breeding 

 new resistant commercial varieties to replace 

 those now being removed. For the purpose 

 of discovering such resistant varieties or spe- 

 cies of Ribes, inoculations under controlled 

 conditions have been made du;i;ing the past 

 three years on 82 varieties of cilltivated red, 

 black and white currants, 23 varieties of culti- 

 vated gooseberries, and 48 species and hybrids 

 of Ribes from various parts of the world. 

 Field tests are also being made with many of 

 the above varieties and species. 



The varieties of a cultivated species show 

 considerable variation in the degree of their 

 susceptibility to the disease. The cultivated 

 species of Ribes also vary decidedly in sus- 

 ceptibility. Some varieties and some species, 

 notably Ribes nigrum, are very congenial 

 hosts for the rust, very abundant uredinia and 

 telia being produced thereon. In other vari- 

 eties and species the rust spreads rapidly over 

 the leaf surface and produces abundant ure- 

 dinia, but the leaf tissue often dies before 

 many telia are formed. In other cases a 

 few uredinia form, at which time irregular 

 areas of the leaf tissue die quickly, with or 

 without further spread of the fungus around 

 the dead area. Sometimes, instead of a defi- 

 nite area being killed, small streaks or flecks 

 are killed. These dead spots often enlarge 

 slowly, producing occasionally a few uredinia 

 or telia. All intergradations are found be- 

 tween R. nigrum, upon which the maximum 

 number of fruiting bodies form, and R. leptan- 

 thum, on which small dead areas and flecks 

 are formed, on less than 10 per cent, of which 

 rust spores are produced. The vigor of the 

 plant and the age of the leaves have an in- 

 fluence on the development of the disease. The 



