112 DISEASES OF GLASSHOUSE PLANTS 
produced on the upper surface of the leaves, varying in 
diameter from an eighth of an inch to patches covering 
half the leaf. (Fig. 32). The tissue round the spots turns 
yellow, and, as the spots become old, minute dark pycnidia 
or fruiting bodies are distributed over the surface. Ulti- 
mately the leaves fall, and as the diseased plants lose 
their foliage they become weakened and stunted blooms 
are produced. 
On the diseased areas conidia are produced in great 
abundance during the sum- 
mer and autumn months, 
and in consequence any 
new foliage is quickly in- 
fected. Infected leaves 
may remain green through 
the winter and so carry the 
infection over to the next 
season. Mrs. Alcock (1) 
has shown also that in this 
country the fungus may 
hibernate on the young 
, wood of the previous 
season. On such parts she 
found discoloured areas, 
which on examination 
proved to contain abund- 
ant mycelium, and compact 
Fie. 32. Rose leaf blotch: (a) Diseased b ‘ 
leaf, (b) spore cluster, (¢) spores. fungal masses bearing in- 
numerable spores of the leaf blotch parasite. 
This discovery is of considerable importance as 
affecting methods of control for this disease. Not only 
must all infected leaves be removed from the tree or 
collected from the ground at the base and burned, but 
attention must be paid to the fungal patches occurring 
on the new wood. ‘These should be removed by pruning, 
but the operation must be conducted judiciously, in 
accordance with the requirements of the variety. So 
far as is known, the old pustules on two-year-old wood 
