469 
THE WHITE RUST AND OTHER MICROSCOPIC 
FUNGI. 
BY M. C. COOKE. 
O ECENT investigations, conducted by Dr. A. de Bary, 
It on this and some other allied Fungi, have produced 
such, important results, that it becomes necessary, in further- 
ance of our design to render familiar the structure and 
vegetation of these minute organisms, to devote ourselves 
to an explanation of what this eminent mycologist has done 
in extending knowledge in this direction. What is the ex- 
ternal appearance presented by the “ white rust " of cabbages, 
and allied cruciferous plants, is soon told. At the present 
season, and for two months past, it has, and continues to 
occupy the surface of the leaves and stems of the shepherds 
purse ( Gapsella bursct-pastdris) , with elongated narrow white 
spots like streaks of whitewash, and now the leaves of the 
goat's beard have commenced to be similarly infected. This 
has been called the “ white rust and later in the season the 
leaves of cauliflowers and cabbages will become ornamented 
with similar patches, arranged in a circular manner, forming 
spots as large as a sixpence. Wherever these spots appear 
the plant is more or less deformed, swollen, or blistered, even 
before the parasite makes its appearance at the surface. These 
white pustules have a vegetative system of ramifying threads 
which traverse the internal portion of the plants on which they 
are found ; these threads constitute what is termed the mycelium. 
Not only when the plant is deformed and swollen with its 
undeveloped parasite do we meet with the threads of mycelium 
in its internal structure, but also in apparently healthy portions 
of the plant, far removed from the evidently infected spots. 
These threads are unequal in thickness, much branched, and 
often with thick gelatinous walls filled with a colourless fluid. 
They creep insidiously along the intercellular passages, and are 
provided with certain appendages in the form of straight 
thread-like tubes, swollen at their tips into globular vesicles. 
These threads do not exceed in length the diameter of the 
mycelium which bears them. The appendages communicate 
in their interior with the mycelium and contain within them 
the same fluid, which at length becomes more watery, and the 
