124 
W. T. THISELTON DYER. 
passing over it, sends down into it» opening a lateral branch. 
The mycelial filaments, however derived, now enter the 
intercellular air passages of the leaf and immediately alter 
their habit of growth. From being slender, filamentous, and 
attenuated, they become thicker, more copiously furnished 
with short branches, and exhibiting, in fact, what has been 
called the coral- like habit” (PL XII, fig. 1, g). They 
excavate the parenchymatous tissue bounding the inter- 
cellular air passages, which is, of course, to attack the plant 
in a most vital and important point. The branches may be 
seen to impinge on one of the chlorophyll-containing and 
starch-forming cells, the wall undergoes absorption, and the 
contents are speedily evacuated. These injuries being in- 
flicted when the leaf is still young and its new foliage 
scarcely matured, the lesion appears to cause a disturbance 
of the health of the leaf, at first sight scarcely explicable 
by the comparatively small proportion which the tissues 
actually destroyed bear to those which are unaffected. But 
the internal cavities produced intercept the paths taken 
towards the plant by the carbohydrates fabricated by the 
leaf, and towards the leaves by the water charged with saline 
matter brought up to them from the roots. The functions 
of the leaves are completely disorganised, and, as always 
happens when this is the case, when the struggle ceases any 
longer to be possible, they are shed. 
The young shoots which bear the new foliage commonly 
perish, and, at any rate, the coffee berries which they bear 
are not matured ; those on the older part of the branches 
are badly developed, and the crop is both reduced and de- 
teriorated by the admixture of ill-developed berries. The 
effect upon the coffee industry has been very serious. Mr. 
Abbay estimates that up to 1871 the average yield for five 
years over the whole of Ceylon had been 4*5 cwt. per acre, 
whilst for the five succeeding years the average has only 
been 2*9 cwt. For the ten years during which the disease 
had existed from 1869 to 1878 he estimated the total loss 
in crops alone due to the disease as from £12,000,000 to 
£15,000,000. 
In order to conclude the preceding sketch of the life- 
history of the Hemileiuj it is only necessary to add that, after 
feeding for some time on the leaf tissues, the mycelial 
filaments send off lateral branches into the air chambers 
beneath the stomata, and the aggregation of these grow up 
side by side in a closely compacted bundle. On emerging 
from the mouth of the stomata each filament develops from 
its apex a sporangium. The object of this process of fructi- 
