E. J. BUTLER 13 



clue to the much, greater length of time occupied in conveying 

 the coffee seeds or bushes to that part of the workl when first 

 introduced, and the comparative rarity of intercourse between 

 the two areas. 



The hollyhock rust is an even more striking case of distribution 

 over distant areas before it reached those nearer at hand. It 

 is endemic in Chile and was first collected there before 1831. 

 It is said to have been seen near Melbourne in Australia in 

 1857 and was certainly collected in 1865. In 1869, it was 

 found in Spain and reached France in 1872 or 1873. In 

 1873, it was widely distributed in France, had appeared in 

 several places in England and was found in Eastadt in 

 Germany. In 1874, it was all over Holland, in Stuttgart, 

 Erlangen, Nurenberg and Lubeck in Germany, near Rome and 

 Naples and in Denmark. In 1875, it reached the Cape of Good 

 Hope ; in 1876, Austria, Hungary and Russia ; 1877, Switzerland 

 and Greece ; 1887, Sweden ; and 1890, Finland. Up to 1886 it 

 was unknown in the United States but in that year it was 

 found in Massachusetts and soon spread to other States. It 

 was, when first introduced to Europe, exceedingly destructive 

 and even now, though less virulent, little liable to be over- 

 looked. Though not well suited for wind dissemination, as its 

 spores are not set free as readily as in most of the other cases 

 discussed, still they are eventually liberated in considerable 

 quantities with fragments of the plant, and if liable to wind 

 dispersal over long distances it is remarkable that the United 

 States should have escaped so long after the fungus had 

 reached Europe and Australia from Chile. It appears to travel 

 really with seed. 



The above cases have been given at some length as they are all noticeable 

 or destructive diseases whose spread has attracted attention. In most of 

 them the parasite liberates its spores into the air, sometimes in great quantity 

 but in none that I have been able to find is there the slightest evidence that 

 the spores can cross the oceans borne by the wind. Several suggest that aerial 

 spread is limited to a few miles, while others are capable of bigger jumps, 

 possibly of 50 miles or (oak mildew) even more.^ 



1 I have purposely left out of consideration whether wo can ofTer any explanation why 

 the spores of a particular disease are not carried successfully over long distances in the air. The 

 problem is, are they carried or not ; and if not, the reasons why do not concern us. 



