466 SCIEXCE PROGRESS. 



of Mauritius with a mouse disease — without apparent 

 success.^ 



Nothing appears to be done in the way of encouraging 

 the various enemies of the moth-borer. The small egg- 

 destroying Hyinenoptera may be left to their good work, 

 but no means suggests itself of increasing their powers. 

 An attempt has been made by Watts to inoculate the moth- 

 borer caterpillars in Antigua with the spores of Isaria 

 Barberi and also of Botrytis tenella received from Giard in 

 Paris. "^ Similar attempts have been made with Java moth- 

 borers, and by Kobus with the beetle Wawalan.^ These 

 have not thus far proved successful. It seems, after all, as 

 if little, if anything, can be accomplished along this line of 

 attack. The mutual relations of the various members 

 living in any one district must be much more clearly traced : 

 the laws by which certain forms suddenly increase out of all 

 proportion and without apparent reason during a single 

 season : the conditions which lead to their almost total des- 

 truction by parasites — all these must be better understood 

 before we can hope to sow diseases and call epidemics into 

 being, and by this means protect our cultivated plants from 

 their parasites. 



5. A useful defensive measure is sometimes found in 

 the careful demarcation of disease areas and the observance 

 of strict quarantine. The introduction of plants from one 

 region to another is rendered dangerous by the remarkable 

 fact that the diseases which attack cultivated plants in one 

 country are frequently harmless in others and vice versa, — that 

 the virulence of a disease in any one plant varies with the 

 locality as well as at different times in the same locality. 

 Great care is therefore necessary lest the importation of 

 new varieties into any district should lead to the introduc- 

 tion of new diseases. A striking warning is met with in 

 the history of the replacement of European vines by 

 American ones. The leaves of the latter were found to 

 be more resistant to the vine mildew {Oidiiuu Tuckeri), and 

 were consequently introduced into Europe."* The appear- 

 ance of these American vines in Europe was followed, in 

 ^ Boname. -Ciiard; Wakker. ^ Kobus (2), (3) ; Wakker. * Esser. 



