eee SF es Se ees Roa st 
BORTHWICK AND WILSON—Two Rust DISEASES OF SPRUCE. 67 
flattened side, 20-24 x 20-23 mw in size. The wall is strongly 
verrucose and pitted except at the flattened portion; fig. 
shows a spore in surface view, and fig. 5 one in optical section. 
The peculiar flattening of the aecidiospore depends on its 
method of development. A number of rows of cells are produced 
in the young aecidium, and in each row only every alternate 
cell gives rise to a spore. The intermediate cells which do not 
produce spores remain thin-walled and at maturity become 
gelatinous and almost disappear. The flattened part of the wall 
of the aecidiospore is the portion which was originally in contact 
with the intermediate cell below it, and, in some cases, the 
shrivelled remains of this cell are still attached and may be seen 
as a black line when the aecidiospore is seen in optical section 
(fig. 5). 
In districts where the spruce does not occur it is probable 
that the fungus may exist through the winter in the form of 
hibernating uredospores, which, in the following spring, can 
infect the Rhododendron ; it appears therefore that the presence 
of the spruce is not essential to the continued existence of the 
fungus. The aecidial stage on the spruce, however, can only 
exist where the Rhododendron is present, as the infection of 
the needles is only brought about by the sporidia. Since this is 
the case, the removal of the Rhododendron will completely 
check the disease. 
It appears, therefore, that the spread of the disease on the 
spruce will be limited in this country since Rhododendron 
hirsutum and R. ferrugineum, although frequent in parks and 
gardens, are not usually grown in plantations. The fungus 
has been found on R. dahuricum, but does not attack R. ponticum, 
R. catawbiense, and their hybrids which are so commonly grown. 
The effect of the disease on the Rhododendron is not serious ; 
on the spruce the diseased needles fall in the summer of infection, 
and in severe cases the trees may be almost stripped of foliage. 
Chrysomyxa abietis, Wallr. The Needle Rust of the Spruce. 
Chrysomyxa abietis was first recorded in Scotland by Somer- 
ville,* from Durris near Aberdeen, and, writing in January 1915, 3 
the same investigator stated that up to that time he had received 
no further reports of its occurrence. A quantity of the fungus 
was recently obtained from Aberdeenshire, and in view of the 
omission of this species from recent works on British Uredineae 
as well as its importance as a disease of the spruce, further in- 
quiries as to its distribution in Scotland have been made. 
* Quart. Journ. Forestry, vol. v, I91I, p. pig 
+ Quart. Journ. Forestry, vol. ix, 1915, P- 
