THE COFFEE-LEAF DISEASE OF CEYLON. 
129 
left their banana sulus on the ground, and were thoroughly 
washed in the river before they could get near the boat. 
The Europeans walked into the river, where they and 
their clothes were thoroughly washed before entering the 
boat to put on clean clothes. By these means the camp 
was kept as clean as possible under the circumstances, as 
this method was rigidly carried out.” 
The whole of the infected coffee was burned with all the 
herbage on the ground which could retain the sporangia, and 
additional fuel was carried on to the ground where necessary, 
so as to enable a continuous wave of flame to pass over it. 
The extraordinary prominence which the Hemileia has 
suddenly assumed is at first sight not a little astonishing ; 
but the ravages of pai*asitic upon cultivated plants, it is not 
difficult to see is one of the consequences with which we 
have to reckon in disturbing the established order of nature. 
Hemileia vastatrix is a parasitic plant which has probably 
for ages lived in a state of constrained commensalism with 
some other members of the family of Hubiacecey to which 
coffee belongs. The constituents of tropical forests are not 
gregarious ; the native host of the Hemileia is, perhaps, some 
plant of little but botanical interest, of which individuals 
- are scattered at intervals through the forest. Parasitic 
plants in nature obviously cannot extirpate their hosts, 
because, if they did so, they would determine their own ex- 
tinction. They only exist at all, therefore, by doing the 
minimum of injury to their hosts which is compatible with 
their own continued existence. But when man places 
within their reach vast aggregations of plants ready for in- 
vasion the latent capacity for mischief of the parasite is 
brought out to the uttermost, and it runs riot at man’s ex- 
pense. If Ceylon were abandoned to nature the coffee planta- 
tions would lapse again into mixed forest ; coffee would 
either succumb to the Hemileiay or would only be repre- 
sented by those individuals which proved able to carry on a 
commensal existence with it. 
It is remarkable that though the coffee districts of the 
New World are free so far from the Hemileiay they are 
also ravaged by a leaf disease. In this also the parenchyma 
of the leaf is devoured and destroyed with parallel consti- 
tutional effects. The parasite is, however, in this case not 
a fungus but the larvae of a minute moth {Cemiostoma 
coffeellum'). This seems to have first taken to its mis- 
chievous vocation in the West Indian Islands, and thence 
to have been introduced on the South American continent, 
in all the coffee- growing districts of which it is a serious pest. 
