34 Barclay.— On the Life-history of 
stems, and sometimes by considerable hypertrophy of the two 
latter. Invaded leaf-blades are often considerably crumpled 
when extensively attacked : oftener only a portion of the 
blade is involved, and frequently at the base. Petioles are very 
frequently attacked, and are then often hypertrophied. The 
main stalks are not so often attacked, but when this happens 
they are frequently very greatly hypertrophied, especially when 
the attack is at a node (Fig. 7). When the leaf-blade is attacked 
usually very numerous coalescing minute circular pustules are 
formed on the under surface, the upper surface opposite being 
pale or somewhat reddish. When attacked areas are small 
they are usually convex above, the lower concave surface 
bearing the spore-pustules. These spore-pustules are some- 
times so closely aggregated that on superficial examination it 
would appear that the whole patch of spore-extrusion is one 
large spore-bed. Sometimes a few pustules burst from the 
upper leaf surface ; but this is uncommon. When the leaf- 
blade is extensively attacked it is observable that the main 
nerves are thickened, showing a tendency for the mycelium to 
run along the vascular structures. On the petioles and stems 
the pustules are oval, and do not tend to coalesce so readily, 
due, to some extent I believe, to the extension of surface by 
hypertrophy. 
The spores are very deciduous, falling off with only a frag- 
ment of stalk adhering. They are brown, rounded at both 
ends, with little or no constriction at the septum, and very 
uniform in size. The epispore is not thickened anywhere 
(though a very slight colourless tubercle at the free end may 
be seen in most) and is beset over both cells with warts or 
tubercles, not densely aggregated, those over the lower cell 
being somewhat finer than those over the upper (Figs. 2, 3). 
Spores are frequently found divided into three and four cells, 
naturally suggesting a comparison with Phragmidium (Fig. 5). 
Each cell exhibits a well-marked nuclear space. The fresh 
spores just moistened measure 30 x 16 — 18 /x. On germination 
each cell throws out a short colourless promycelium, dividing 
as usual into four parts, each bearing a sporidium at the end 
